Information reproducing apparatus and method, and computer program

ABSTRACT

An information reproducing apparatus ( 1 ) is provided with: a judging device ( 20 ) for judging whether or not a read signal (R RF ) read from a recording medium ( 100 ) satisfies a desired reproduction property; a correcting device ( 18 ) for correcting waveform distortion occurring in a read signal corresponding to a long mark, of the read signal if it is judged that the read signal does not satisfy the desired reproduction property; and a waveform equalizing device ( 15 ) for performing a waveform equalization process on the read signal in which the waveform distortion is corrected.

TECHNICAL FIELD

The present invention relates to an information reproducing apparatus and method which reproduce record data recorded on a recording medium, and particularly relates to an information reproducing apparatus and method which perform waveform equalization, such as a filtering process, on a read signal obtained by reading the record data recorded on the recording medium, as well as a computer program which makes a computer function as the information reproducing apparatus.

BACKGROUND ART

In order to improve an SN ratio of a read signal read from the recording medium on which the data is recorded at high density, there is known a technology by which a filtering process for emphasizing high frequencies is performed on the read signal, for waveform equalization. In particular, according to a patent document 1, it discloses the technology by which the high frequencies can be emphasized without any intersymbol interference by performing the filtering process after amplitude limit is performed on the read signal (a technology about a so-called limit equalizer).

-   Patent document 1: Japanese Patent No. 3459563

DISCLOSURE OF INVENTION Subject to be Solved by the Invention

Here, waveform distortion can occur in the read signal. The waveform distortion indicates such a status that there is a discrepancy between a proper signal level to be taken and a signal level that actually appears in the read signal. If the waveform distortion is included in a range in which the amplitude limit is performed on a limit equalizer (i.e. as coherency between the waveform distortion and an amplitude limit value on the limit equalizer increases), the waveform distortion is further emphasized by high-frequency emphasis performed after the amplitude limit. For example, this likely leads to a disadvantage that a mark with a relatively long run length is misjudged to be another mark. Specifically, for example, this likely leads to a disadvantage that a mark with a run length of 8 T is misjudged to be a mark with a run length of 4 T, a space with a run length of 2 T, and a mark with a run length of 2 T.

In view of the aforementioned conventional problems, it is therefore an object of the present invention to provide an information reproducing apparatus and method which can preferably reproduce the record data even if the waveform distortion occurs, as well as a computer program.

Means for Solving the Subject

The above object of the present invention can be achieved by an information reproducing apparatus provided with: a judging device for judging whether or not a read signal read from a recording medium satisfies a desired reproduction property; a correcting device for correcting waveform distortion occurring in a read signal corresponding to at least a long mark, of the read signal if it is judged by the judging device that the read signal does not satisfy the desired reproduction property; and a waveform equalizing device for performing a waveform equalization process on the read signal in which the waveform distortion is corrected.

The above object of the present invention can be also achieved by an information reproducing method provided with: a judging process of judging whether or not a read signal read from a recording medium satisfies a desired reproduction property; a correcting process of correcting waveform distortion occurring in a read signal corresponding to at least a long mark, of the read signal if it is judged in the judging process that the read signal does not satisfy the desired reproduction property; and a waveform equalizing process of performing a waveform equalization process on the read signal in which the waveform distortion is corrected.

The above object of the present invention can be also achieved by a computer program for reproduction control and for controlling a computer provided in an information reproducing apparatus provided with: a judging device for judging whether or not a read signal read from a recording medium satisfies a desired reproduction property; a correcting device for correcting waveform distortion occurring in a read signal corresponding to at least a long mark, of the read signal if it is judged by the judging device that the read signal does not satisfy the desired reproduction property; and a waveform equalizing device for performing a waveform equalization process on the read signal in which the waveform distortion is corrected, the computer program making the computer function as at least one portion of the judging device, the correcting device, and the waveform equalizing device.

The operation and other advantages of the present invention will become more apparent from the embodiments described below.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram conceptually showing the basic structure of an information reproducing apparatus in an example.

FIG. 2 is a block diagram conceptually showing the structure of a limit equalizer in the example.

FIG. 3 is a waveform chart conceptually showing an operation of setting the upper limit and the lower limit of an amplitude limit value, on a sample value series.

FIG. 4 are waveform charts conceptually showing an operation of obtaining a high-frequency emphasized read sample value series, on the sample value series.

FIG. 5 are waveform charts conceptually showing a first example of waveform distortion.

FIG. 6 are waveform charts conceptually showing a second example of waveform distortion.

FIG. 7 is a flowchart conceptually showing a flow of operations of a waveform distortion correction circuit.

FIG. 8 is a block diagram conceptually showing the structure of the waveform distortion correction circuit.

FIG. 9 is a waveform chart conceptually showing an operation of correcting the waveform distortion by the waveform distortion correction circuit, on the sample value series.

FIG. 10 is a waveform chart conceptually showing a waveform or the like of a read signal before and after the correction of the waveform distortion.

FIG. 11 are waveform charts conceptually showing the operation of obtaining the high-frequency emphasized read sample value series, on the sample value series, in each of a case where the waveform distortion is not corrected and a case where the waveform distortion is corrected.

FIG. 12 is a graph showing a change in symbol error rate with respect to a waveform distortion ratio.

FIG. 13 is a block diagram conceptually showing the structure of a waveform distortion correction circuit provided for an information reproducing apparatus in a first modified example.

FIG. 14 is a block diagram conceptually showing the structure of a waveform distortion detection circuit provided for the waveform distortion correction circuit provided for the information reproducing apparatus in the first modified example.

FIG. 15 is a flowchart conceptually showing a flow of operations of the information reproducing apparatus in the first modified example.

FIG. 16 is a flowchart conceptually showing a flow of operations of an information reproducing apparatus in a second modified example.

FIG. 17 is a timing chart conceptually showing an operation of correcting the waveform distortion by a waveform distortion correction circuit provided for an information reproducing apparatus in a third modified example, on a first read signal.

FIG. 18 is a timing chart conceptually showing the operation of correcting the waveform distortion by the waveform distortion correction circuit provided for the information reproducing apparatus in the third modified example, on a second read signal.

FIG. 19 is a flowchart conceptually showing a first flow of operations by the waveform distortion correction circuit provided for the information reproducing apparatus in the third modified example.

FIG. 20 is a flowchart conceptually showing a second flow of operations by the waveform distortion correction circuit provided for the information reproducing apparatus in the third modified example.

FIG. 21 is a flowchart conceptually showing a third flow of operations by the waveform distortion correction circuit provided for the information reproducing apparatus in the third modified example.

FIG. 22 is a waveform chart conceptually showing an operation of correcting the waveform distortion by a waveform distortion correction circuit provided for an information reproducing apparatus in a fourth modified example, on the sample value series.

FIG. 23 is a block diagram conceptually showing the structure of the waveform distortion correction circuit provided for the information reproducing apparatus in the fourth modified example.

FIG. 24 is a waveform chart conceptually showing an operation of correcting the waveform distortion by a waveform distortion correction circuit provided for an information reproducing apparatus in a fifth modified example, on the sample value series.

FIG. 25 is a block diagram conceptually showing the structure of the waveform distortion correction circuit provided for the information reproducing apparatus in the fifth modified example.

FIG. 26 is a waveform chart conceptually showing an operation of correcting the waveform distortion by a waveform distortion correction circuit provided for an information reproducing apparatus in a sixth modified example, on the sample value series.

FIG. 27 is a block diagram conceptually showing the structure of the waveform distortion correction circuit provided for the information reproducing apparatus in the sixth modified example.

FIG. 28 is a waveform chart conceptually showing an operation of correcting the waveform distortion by a waveform distortion correction circuit provided for an information reproducing apparatus in a seventh modified example, on the sample value series.

FIG. 29 is a block diagram conceptually showing the structure of the waveform distortion correction circuit provided for the information reproducing apparatus in the seventh modified example.

FIG. 30 are graphs showing a change in symbol error rate with respect to asymmetry, in each of a case where the amplification factor of a pre-equalizer provided for an information reproducing apparatus in an eighth modified example is increased and a case where the amplification factor is not increased.

FIG. 31 are graphs showing a change in symbol error rate with respect to the amplification factor of the pre-equalizer, in each of a case where the waveform distortion is corrected and a case where the waveform distortion is not corrected.

FIG. 32 is a waveform chart conceptually showing a waveform of the read signal corresponding to mini according to a change in asymmetry.

FIG. 33 is a waveform chart conceptually showing another waveform or the like of the read signal before and after the correction of the waveform distortion.

FIG. 34 is a block diagram conceptually showing the basic structure of an information reproducing apparatus in a ninth modified example.

FIG. 35 is a waveform chart conceptually showing an asymmetry value.

FIG. 36 are graphs showing a change in symbol error rate with respect to an offset value normalized by the amplitude of the read signal.

FIG. 37 are graphs showing a change in the offset value normalized by the amplitude of the read signal, with respect to the asymmetry value.

FIG. 38 are tables showing the appearance probability of the record data with each run length.

FIG. 39 is a waveform chart conceptually showing an entire β value.

FIG. 40 is a graph showing a change in the offset value normalized by the amplitude of the read signal, with respect to the entire β value normalized by the amplitude of the read signal.

FIG. 41 is a waveform chart conceptually showing a partial β value.

FIG. 42 is a graph showing a change in the offset value normalized by the amplitude of the read signal, with respect to the partial β value normalized by the amplitude of the read signal.

FIG. 43 is a waveform chart conceptually showing an α value.

FIG. 44 is a block diagram conceptually showing the basic structure of an information reproducing apparatus in a tenth modified example.

FIG. 45 are graphs showing a change in symbol error rate with respect to the offset value normalized by the amplitude of the read signal, in each of a case where the offset value is only added (i.e. where the offset value is not subtracted) and a case where the offset value is added and subtracted.

FIG. 46 is a plan view schematically showing marks on a recording surface of a read-only type optical disc.

DESCRIPTION OF REFERENCE CODES

-   1, 2 information reproducing apparatus -   10 spindle motor -   11 pickup -   12 HPF -   13 AID converter -   14 pre-equalizer -   15 limit equalizer -   16 binary circuit -   17 decoding circuit -   18 waveform distortion correction circuit -   181 delay adjustment circuit -   182 distortion-correction-value detection circuit -   183 mark/space length detection circuit -   184 timing generation circuit -   185 selector -   186 waveform distortion detection circuit -   19-1 i adder -   19-2 i offset generation circuit -   19-3 subtracter -   151 amplitude limit value setting block -   1516 averaging circuit -   152 amplitude limit block -   1522 interpolation filter -   1523 limiter -   153 high-frequency emphasis block -   20 reproduction property judgment circuit

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, as the best mode for carrying out the present invention, an explanation will be given on embodiments of the information reproducing apparatus and method, and the computer program of the present invention.

(Embodiment of Information Reproducing Apparatus)

An embodiment of the information reproducing apparatus of the present invention is an information reproducing apparatus provided with: a judging device for judging whether or not a read signal read from a recording medium satisfies a desired reproduction property; a correcting device for correcting waveform distortion occurring in a read signal corresponding to at least a long mark, of the read signal if it is judged by the judging device that the read signal does not satisfy the desired reproduction property; and a waveform equalizing device for performing a waveform equalization process on the read signal in which the waveform distortion is corrected.

According to the embodiment of the information reproducing apparatus of the present invention, by the operation of the judging device, it is judged whether or not the read signal satisfies the desired reproduction property. The desired reproduction property will be detailed later.

Then, by the operation of the correcting device, the waveform distortion is corrected which occurs in the read signal corresponding to at least the long mark (e.g. marks with run lengths of 7 T to 11 T and 14 T if the recording medium is a DVD, and marks with run lengths of 6 T to 9 T if the recording medium is a Blu-ray Disc). Here, the waveform distortion (and more specifically, for example, the signal level or the like of the waveform distortion) is preferably corrected such that the waveform distortion does not have an adverse effect on the waveform equalization by the waveform equalizing device (and specifically, for example, on amplitude limit and high-frequency emphasis filtering described later).

Then, by the operation of the waveform equalizing device, the waveform equalization process is performed on the read signal in which the waveform distortion is corrected. Then, various signal processes (e.g. a binary process, a decoding process, and the like) are performed on the waveform-equalized read signal, and thus, the record data is reproduced.

In particular, in the embodiment, the waveform distortion is selectively corrected by the correcting device when it is judged by the judging device that the read signal does not satisfy the desired reproduction property. Here, in particular, as opposed to the recording medium which allows only sequential recording, various recording statuses are mixed in the recording medium which allows random recording. In this case, it is necessary to read the read signal in which the waveform distortion is discontinuously or discretely distributed or not distributed, or to read the read signal which has various signal levels. Therefore, by reproducing the record data without correcting the waveform distortion in a normal case, and by reproducing the record data while selectively correcting the waveform distortion in the aforementioned cases, it is possible to receive the aforementioned various effects while reducing a load of the information reproducing apparatus.

As described above, according to the information reproducing apparatus in the embodiment, even if the waveform distortion occurs, the waveform equalization can be excellently performed while excellently performing the amplitude limit. As a result, even if the waveform distortion occurs, the record data can be preferably reproduced.

In another aspect of the embodiment of the information reproducing apparatus of the present invention, it is further provided with a detecting device for detecting the waveform distortion, the correcting device correcting the waveform distortion if it is judged by the judging device that the read signal does not satisfy the desired reproduction property and if the waveform distortion is detected by the detecting device.

According to this aspect, the waveform distortion is corrected selectively when the waveform distortion is detected. Therefore, it is possible to receive the aforementioned various effects while reducing the load of the information reproducing apparatus.

In another aspect of the embodiment of the information reproducing apparatus of the present invention, the judging device judges that the read signal satisfies the desired reproduction property in at least one of (i) a case where an error correction of the read signal (more specifically, an error correction of the record data obtained from the read signal) cannot be performed, (ii) a case where an error rate of the read signal (more specifically, an read error rate of the record data obtained from the read signal) is greater than or equal to a predetermined threshold value, or (iii) a case where a read signal corresponding to synchronization data cannot be read, the synchronization data being used to read user data included in record data, the synchronization data being included in the record data.

According to this aspect, it is possible to preferably judge whether or not the read signal satisfies the desired reproduction property.

In another aspect of the embodiment of the information reproducing apparatus of the present invention, the judging device judges whether or not the read signal satisfies the desired reproduction property after the waveform distortion is corrected by the correcting device, and the correcting device corrects the waveform distortion again if it is judged again by the judging device that the read signal does not satisfy the desired reproduction property.

According to this aspect, the waveform distortion is corrected until the desired reproduction property is satisfied. Thus, this results in so-called retrying the reading of the read signal until the desired reproduction property is satisfied, and this allows a more preferable reproduction operation to be performed.

In an aspect of the information reproducing apparatus in which the waveform distortion is corrected again if it is judged again that the read signal does not satisfy the desired reproduction property, as described above, the correcting device may correct the waveform distortion again by using a second waveform distortion correction condition which is different from a first waveform distortion correction condition used when the waveform distortion is corrected at a previous time, if it is judged again by the judging device that the read signal does not satisfy the desired reproduction property.

By virtue of such construction, since the waveform distortion is corrected while changing the waveform distortion correction condition as occasion demands, it is possible to preferably correct the waveform distortion.

In another aspect of the embodiment of the information reproducing apparatus of the present invention, the correcting device corrects the waveform distortion occurring in the read signal corresponding to synchronization data, the synchronization data being used to read user data included in record data, the synchronization data being included in the record data.

According to this aspect, the read signal corresponding to the synchronization data which is important in reproducing the record data can be at least certainly read, so that the record data can be preferably reproduced.

In an aspect of the information reproducing apparatus in which the waveform distortion is corrected which occurs in the read signal corresponding to the synchronization data, as described above, the correcting device may correct the waveform distortion at least one of before a space which makes a pair with a mark which constitutes the synchronization data of the read signal, after the space, and at a position which satisfies periodicity of the synchronization data, with a base point at the space. Specifically, for example, if the recording medium is a Blu-ray Disc, the correcting device may correct the waveform distortion at least one of before a space with a run length of 9 T which makes a pair with a mark with a run length of 9 T which constitutes the synchronization data of the read signal, after the 9 T space, and at a position after a lapse of a time corresponding to a run length of about 1932 T from the 9 T space. Alternatively, for example, if the recording medium is a DVD, the correcting device may correct the waveform distortion at a position after a lapse of a time corresponding to a run length of about 1488 T from a space with a run length of 14 T which constitutes the synchronization data of the read signal.

By virtue of such construction, focusing on the periodicity that the synchronization data appears, it is possible to correct the waveform distortion in the read signal corresponding to the synchronization data, relatively easily.

In another aspect of the embodiment of the information reproducing apparatus of the present invention, the waveform equalizing device is provided with: an amplitude limiting device for limiting an amplitude level of the read signal in which the waveform distortion is corrected, by a predetermined amplitude limit value, thereby obtaining an amplitude limit signal; and a filtering device for performing a high-frequency emphasis filtering process on the amplitude limit signal, thereby obtaining an equalization-corrected signal.

According to this aspect, by the operation of the amplitude limiting device, the amplitude level of the read signal in which the waveform distortion is corrected (hereinafter referred to as a “distortion-corrected signal”, as occasion demands) is limited. Specifically, with respect to a signal component of the distortion-corrected signal whose amplitude level is greater than the upper limit of the amplitude limit value or is less than the lower limit of the amplitude limit value, the amplitude level is limited to the upper limit or the lower limit of the amplitude limit value. On the other hand, with respect to a signal component of the distortion-corrected signal whose amplitude level is less than or equal to the upper limit of the amplitude limit or is greater than or equal to the lower limit of the amplitude limit value, its amplitude level is not limited. The distortion-corrected signal in which the amplitude level is limited as described above is outputted to the filtering device as the amplitude limit signal. On the filtering device, the high-frequency emphasis process is performed on the amplitude limit signal. As a result, the equalization-corrected signal is obtained. Then, for example, a binary process, a decoding process, and the like are performed on the equalization-corrected signal. By this, a process of reproducing the record data (e.g. video data, audio data, and the like) recorded on the recording medium can be performed.

By this, on the filtering device, it is possible to limit or control the occurrence of the dispersion (i.e. jitter) of the read signal (or its sample values), and as a result, it is possible to perform the high-frequency emphasis on the read signal without any intersymbol interference.

Moreover, since the waveform distortion occurring in the read signal is corrected before the waveform equalization process is performed by the waveform equalizing device, the waveform distortion hardly has or does not have an adverse effect on the amplitude limit and the high-frequency emphasis filtering even if the waveform distortion occurs in the read signal read from the recording medium. More specifically, for example, it is possible to preferably prevent such a disadvantage that the waveform distortion is further emphasized, which is caused by that the waveform distortion is less than or equal to the upper limit of the amplitude limit value or is greater than or equal to the lower limit of the amplitude limit value. In other words, by correcting the waveform distortion, it is possible to keep the coherency between the waveform distortion and the amplitude limit value at low level. As a result, for example, it is possible to preferably prevent such a disadvantage that the long mark is misjudged to be another mark. By this, on the limit equalizer (i.e. the amplitude limiting device and the filtering device), the high-frequency emphasis can be preferably performed on the read signal.

In another aspect of the embodiment of the information reproducing apparatus of the present invention, the long mark is a mark whose signal level is maximum amplitude.

According to this aspect, it is possible to preferably correct the waveform distortion occurring in the read signal corresponding to the long mark.

(Embodiment of Information Reproducing Method)

An embodiment of the information reproducing method of the present invention is an information reproducing method provided with: a judging process of judging whether or not a read signal read from a recording medium satisfies a desired reproduction property; a correcting process of correcting waveform distortion occurring in a read signal corresponding to at least a long mark, of the read signal if it is judged in the judging process that the read signal does not satisfy the desired reproduction property; and a waveform equalizing process of performing a waveform equalization process on the read signal in which the waveform distortion is corrected.

According to the embodiment of the information reproducing method of the present invention, it is possible to receive the same various effects as those that can be received by the aforementioned embodiment of the information reproducing apparatus of the present invention.

Incidentally, in response to the various aspects in the aforementioned embodiment of the information reproducing apparatus of the present invention, the embodiment of the information reproducing method of the present invention can also adopt various aspects.

(Embodiment of Computer Program)

An embodiment of the computer program of the present invention is a computer program for reproduction control and for controlling a computer provided in an information reproducing apparatus provided with: a judging device for judging whether or not a read signal read from a recording medium satisfies a desired reproduction property; a correcting device for correcting waveform distortion occurring in a read signal corresponding to at least a long mark, of the read signal if it is judged by the judging device that the read signal does not satisfy the desired reproduction property; and a waveform equalizing device for performing a waveform equalization process on the read signal in which the waveform distortion is corrected (i.e. the aforementioned embodiment of the information reproducing apparatus of the present invention (including its various aspects)), the computer program making the computer function as at least one portion of the judging device, the correcting device, and the waveform equalizing device.

According to the embodiment of the computer program of the present invention, the aforementioned embodiment of the information reproducing apparatus of the present invention can be relatively easily realized as a computer reads and executes the computer program from a program storage device, such as a ROM, a CD-ROM, a DVD-ROM, and a hard disk, or as it executes the computer program after downloading the program through a communication device.

Incidentally, in response to the various aspects in the aforementioned embodiment of the information reproducing apparatus of the present invention, an embodiment of the computer program product of the present invention is a computer program product in a computer-readable medium for tangibly embodying a program of instructions executable by a computer provided in an information reproducing apparatus provided with: a judging device for judging whether or not a read signal read from a recording medium satisfies a desired reproduction property; a correcting device for correcting waveform distortion occurring in a read signal corresponding to at least a long mark, of the read signal if it is judged by the judging device that the read signal does not satisfy the desired reproduction property; and a waveform equalizing device for performing a waveform equalization process on the read signal in which the waveform distortion is corrected (i.e. the aforementioned embodiment of the information reproducing apparatus of the present invention (including its various aspects)), the computer program making the computer function as at least one portion of the judging device, the correcting device, and the waveform equalizing device.

According to the embodiment of the computer program product of the present invention, the aforementioned embodiment of the information reproducing apparatus of the present invention can be embodied relatively readily, by loading the computer program product from a recording medium for storing the computer program product, such as a ROM (Read Only Memory), a CD-ROM (Compact Disc-Read Only Memory), a DVD-ROM (DVD Read Only Memory), a hard disk or the like, into the computer, or by downloading the computer program product, which may be a carrier wave, into the computer via a communication device. More specifically, the computer program product may include computer readable codes to cause the computer (or may comprise computer readable instructions for causing the computer) to function as the aforementioned embodiment of the information reproducing apparatus of the present invention.

Incidentally, in response to the various aspects in the aforementioned embodiment of the information reproducing apparatus of the present invention, the embodiment of the computer program product of the present invention can also employ various aspects.

The operation and other advantages of the present invention will become more apparent from the examples explained below.

As explained above, according to the embodiment of the information reproducing apparatus of the present invention, it is provided with the judging device, the correcting device, and the waveform equalizing device. According to the embodiment of the information reproducing method of the present invention, it is provided with the judging process, the correcting process, and the waveform equalizing process. According to the embodiment of the computer program of the present invention, it makes a computer function as the embodiment of the information reproducing apparatus of the present invention. Therefore, it is possible to preferably reproduce the data even if the waveform distortion occurs.

Examples

Hereinafter, an example of the present invention will be described on the basis of the drawings.

(1-1) Basic Structure

Firstly, with reference to FIG. 1, an example of the information reproducing apparatus of the present invention will be described. FIG. 1 is a block diagram conceptually showing the basic structure of the information reproducing apparatus in the example.

As shown in FIG. 1, an information reproducing apparatus 1 in the example is provided with a spindle motor 10, a pickup (PU) 11, a HPF (High Pass Filter) 12, an A/D converter 13, a pre-equalizer 14, a limit equalizer 15, a binary circuit 16, a decoding circuit 17, a waveform distortion correction circuit 18, and a reproduction property judgment circuit 20.

The pickup 11 photoelectrically converts reflected light when a laser beam LB is irradiated to a recording surface of an optical disc 100 rotated by the spindle motor 10, thereby generating a read signal R_(RF).

The HPF 12 removes a low-frequency component of the read signal R_(RF) outputted from the pickup, and it outputs a resulting read signal R_(HC) to the A/D converter 13.

The A/D converter 13 samples the read signal in accordance with a sampling clock outputted from a PLL (Phased Lock Loop) not illustrated or the like, and it outputs a resulting read sample value series RS to the pre-equalizer 14.

The pre-equalizer 14 removes intersymbol interference based on transmission characteristics in an information reading system, which is formed of the pickup 11 and the optical disc 100, and it outputs a resulting read sample value series RS_(C) to the waveform distortion correction circuit 18.

The reproduction property judgment circuit 20 constitutes one specific example of the “judging device” of the present invention. The reproduction property judgment circuit 20 judges whether or not the read signal R_(RF) satisfies a desired reproduction property, on the basis of the output from the decoding circuit 17. The judgment result is outputted to the waveform distortion correction circuit 18.

The waveform distortion correction circuit 18 constitutes one specific example of the “correcting device” of the present invention. The waveform distortion correction circuit 18 corrects waveform distortion occurring in the read sample value series RS_(C) (i.e. waveform distortion occurring in the read signal R_(RF)). A resulting distortion-corrected read sample value series RS_(CAM) is outputted to the limit equalizer 15.

In particular, the waveform distortion correction circuit 18 corrects the waveform distortion occurring in the read sample value series RS_(C) (i.e. the waveform distortion occurring in the read signal R_(RF)) if it is judged by the reproduction property judgment circuit 20 that the read signal R_(RF) does not satisfy the desired reproduction property. In other words, the waveform distortion correction circuit 18 does not correct the waveform distortion occurring in the read sample value series RS_(C) (i.e. the waveform distortion occurring in the read signal R_(RF)) if it is judged by the reproduction property judgment circuit 20 that the read signal R_(RF) satisfies the desired reproduction property.

Incidentally, a specific structure and operations of the waveform distortion correction circuit 18 will be detailed later (refer to FIG. 6 and subsequent drawings).

The limit equalizer 15 performs a high-frequency emphasis process on the distortion-corrected read sample value series RS_(CAM) without increasing the intersymbol interference, and it outputs a resulting high-frequency emphasized read sample value series RS_(H) to the binary circuit 16.

The binary circuit 16 performs a binary process on the high-frequency emphasized read sample value series RS_(H), and it outputs a resulting binary signal to the decoding circuit 17.

The decoding circuit 17 performs a decoding process or the like on the binary signal, and it outputs a resulting reproduction signal to external reproduction equipment, such as a display and a speaker. As a result, data recorded on the optical disc 100 (e.g. video data, audio data, and the like) is reproduced.

Next, with reference to FIG. 2, the more detailed structure of the limit equalizer 15 will be described. FIG. 2 is a block diagram conceptually showing the structure of the limit equalizer 15. As shown in FIG. 2, the limit equalizer 15 is provided with an amplitude limit value setting block 151, an amplitude limit block 152, and a high-frequency emphasis block 153.

The amplitude limit value setting block 151 sets the upper limit and the lower limit of an amplitude limit value which are used on the amplitude limit block 152, on the basis of the distortion-corrected read sample value series RS_(CAM). The amplitude limit block 152 performs an amplitude limit process on the distortion-corrected read sample value series RS_(CAM), on the basis of the upper limit and the lower limit of the amplitude limit value which are set on the amplitude limit value setting block 151. A sample value series RS_(LIM) on which the amplitude limit process is performed is outputted to the high-frequency emphasis block 153. The high-frequency emphasis block 153 performs a filtering process for emphasizing high frequencies, on the sample value series RS_(LIM) on which the amplitude limit process is performed. As a result, the high-frequency emphasized read sample value series RS_(H) is obtained.

More specifically, a reference sample timing detection circuit 1511 detects reference sample timing, on the basis of the distortion-corrected read sample value series RS_(CAM). The detected reference sample timing is outputted to a sample hold circuit 1514 through a delayer 1512 for providing a one-clock delay and an OR circuit 1513. On the sample hold circuit 1514, a sample value series RS_(P) outputted from an interpolation filter 1522 is sampled and held in accordance with the reference sample timing outputted through the delayer 1512 and the OR circuit 1513.

Incidentally, the interpolation filter 1522 performs an interpolation process on the distortion-corrected read sample value series RS_(CAM), thereby generating an interpolated sample value series which is obtained when the read signal R_(RF) read from the optical disc 100 is sampled in the middle timing of the clock timing based on the sampling clock used on the A/D converter 14. The generated interpolated sample value series is included in the distortion-corrected read sample value series RS_(CAM), and it is outputted to a limiter 1523 and the sample hold circuit 1514, as the sample value series RS_(P).

In the read sample value series RS_(P) sampled and held, a reference level Rf is subtracted on a subtracter 1515. Incidentally, if a zero level is used as the reference level Rf, Rf=0. The subtraction result is outputted to an averaging circuit 1516. The averaging circuit 1516 calculates an average value of an absolute value of each of sample values. The calculated average value of sample values is set as the upper limit and the lower limit of the amplitude limit value. Specifically, a value obtained by adding the average value to the reference level is set as the upper limit of the amplitude limit value, and a value obtained by subtracting the average value from the reference level is set as the lower limit of the amplitude limit value. If the zero level is used as the reference level, a value obtained by providing a positive sign for the calculated average value of sample values is set as the upper limit of the amplitude limit value, and a value obtained by providing a negative sign for the calculated average value of sample values is set as the lower limit of the amplitude limit value. In the following explanation, for convenience of explanation, the zero level is used as the reference level Rf.

Specifically, with reference to FIG. 3, an explanation will be given on the upper limit and the lower limit of the amplitude limit value set on the amplitude limit value setting block 151. FIG. 3 is a waveform chart conceptually showing an operation of setting the upper limit and the lower limit of the amplitude limit value, on the distortion-corrected read sample value series RS_(CAM).

FIG. 3 shows the read signal R_(RF) obtained by reading data with a relatively short run length (specifically, data with run lengths of 2 T, 3 T, and 4 T if the optical disc 100 is a Blu-ray Disc) of the read signal; and its distortion-corrected read sample value series RS_(CAM). As shown in FIG. 3, an average value L of absolute values of interpolated sample values (sample values generated on the interpolation filter 1522) located before (i.e. before in terms of time) a zero cross point and interpolated sample values located after (i.e. after in terms of time) the zero cross point is set as the absolute value of the upper value and the lower value of the amplitude limit value. In other words, the upper limit of the amplitude limit value is set as L, and the lower limit of the amplitude limit value is set as −L.

Back in. FIG. 2 again, the limiter 1523 performs amplitude limit on the sample value series RS_(P) on the basis of the upper limit and the lower limit which are set on the amplitude limit value setting block 151. Specifically, if a sample value included in the sample value series RS_(P) is less than the upper limit L and greater than the lower limit −L, the sample value is outputted as the sample value series RS_(LIM) as it is. On the one hand, if a sample value included in the sample value series RS_(P) is greater than or equal to the upper limit L, the upper limit L is outputted as the sample value series RS_(LIM). On the other hand, if a sample value included in the sample value series RS_(P) is less than or equal to the upper limit −L, the lower limit −L is outputted as the sample value series RS_(LIM).

The high-frequency emphasis block 153 increases the signal level of only the sample value series RS_(LIM) corresponding to data with the shortest run length (e.g. the data with a run length of 3 T if the optical disc 100 is a DVD, and the data with a run length of 2 T if the optical disc 100 is a Blu-ray Disc) in the sample value series RS_(LIM).

Specifically, the sample value series RS_(LIM) inputted to the high-frequency emphasis block 153 is inputted to coefficient multipliers 1535 and 1538 having a multiplier coefficient of −k and coefficient multipliers 1536 and 1537 having a multiplier coefficient of k, as it is or through delayers 1532, 1533, and 1534 for providing a one-clock delay. The outputs of the coefficient multipliers 1535, 1536, 1537, and 1538 are added on an adder 1539. The addition result, a high-frequency read sample value RS_(HIG), is added to the distortion-corrected read sample value series RS_(CAM) which is inputted to the adder 1531 through the delayer 1530 for providing a three-clock delay, on the adder 1531. As a result, the high-frequency emphasized read sample value series RS_(H) is obtained.

Now, with reference to FIG. 4, an operation of obtaining the high-frequency emphasized read sample value series RS_(H) will be described in more detail. FIG. 4 are waveform charts conceptually showing the operation of obtaining the high-frequency emphasized read sample value series RS_(H), on the distortion-corrected read sample value series RS_(CAM).

As shown in FIG. 4( a), the high-frequency read sample value RS_(HIG) outputted from the adder 1531 is calculated on the basis of the sample values at respective time points D (−1.5), D(−0.5), D(0.5), and D(1.5) in the sample value series RS_(LIM). Specifically, if the sample values at the respective time points D (−1.5), D(−0.5), D(0.5), and D(1.5) in the sample value series RS_(LIM) are Sip(−1), Sip(0), Sip(1), and Sip(2), then, RS_(HIG)=(−k)×Sip(−1)+k×Sip(0)+k×Sip(1)+(−k)×Sip(2).

At this time, as shown in FIG. 4( b), the sample values Sip(−1) and Sip(0) at the respective time points D(−1.5) and D(−0.5) corresponding to the data with a run length of 2 T are substantially equal to each other. Moreover, the sample values Sip(1) and Sip(2) at the respective time points D(0.5) and D(1.5) corresponding to the data with a run length of 2 T are substantially equal to each other.

Moreover, as shown in FIG. 4( c), the sample values Sip(−1) and Sip(0) at the respective time points D(−1.5) and D(−0.5) corresponding to the data with each of run lengths of 3 T and 4 T are both the upper limit L of the amplitude limit value, due to the amplitude limit by the amplitude limit block 152. In the same manner, the sample values Sip(1) and Sip(2) at the respective time points D(0.5) and D(1.5) corresponding to the data with each of run lengths of 3 T and 4 T are both the lower limit −L of the amplitude limit value, due to the amplitude limit by the amplitude limit block 152. In other words, the dispersion of the sample values before and after the reference sample point is forcibly controlled.

Thus, even if the value of the coefficient k is increased on the coefficient multipliers 1535, 1536, 1537, and 1538 in order to increase the high-frequency emphasis, the high-frequency read sample value RS_(HIG) obtained at the zero cross point D(0) is kept constant. Therefore, the intersymbol interference does not occur. As described above, according to the information reproducing apparatus 1 provided with the limit equalizer 15, the dispersion of the sample values before and after the zero cross point in the read signal, which causes the intersymbol interference, is forcibly controlled in performing the high-frequency emphasis. Thus, even if the sufficient high-frequency emphasis is performed on the high-frequency emphasis block 153, the intersymbol interference does not occur.

In particular, in the information reproducing apparatus 1 in the example, the waveform distortion is corrected, and then, the amplitude limit and the high-frequency emphasis are performed on the limit equalizer 15. Hereinafter, a detailed explanation will be given on specific example of the waveform distortion correction.

(1-2) Waveform Distortion

Firstly, with reference to FIG. 5 and FIG. 6, the waveform distortion will be described. FIG. 5 are waveform charts conceptually showing a first example of waveform distortion. FIG. 6 are waveform charts conceptually showing a second example of waveform distortion.

As shown in FIG. 5( a), the waveform distortion indicates a difference between a proper signal level to be taken and a signal level that actually appears in the read signal R_(RF). The waveform distortion is quantitatively defined by a waveform distortion amount D for the maximum amplitude A of the read signal R_(RF), and a waveform distortion amount D′ which is a signal level from the zero level to the peak of the waveform distortion. In FIG. 5( a), a thick dashed line denotes the proper signal level to be taken when there is no waveform distortion. If there is no waveform distortion, the waveform distortion amount D is obviously zero.

Incidentally, the waveform distortion shown in FIG. 5( a) shows such waveform distortion that the signal level in a middle portion is changed, compared to the signal level in a front edge portion and a rear edge portion of the read signal R_(RF). Apart from such waveform distortion, there can be such waveform distortion that the signal level in the front edge portion and the middle portion is changed, compared to the signal level in the rear edge portion of the read signal R_(RF) as shown in FIG. 5( b); and such waveform distortion that the signal level in the middle edge portion and the rear portion is changed, compared to the signal level in the front edge portion of the read signal R_(RF) as shown in FIG. 5( c). For any waveform distortion, the structure and operation described later can be obviously adopted.

Moreover, in FIG. 5( a) to FIG. 5( c), an explanation was given on the waveform distortion occurring on the optical disc 100 in which the reflectance of the laser beam LB is reduced by forming the marks. In other words, an explanation was given on the example in which the waveform distortion occurs such that the signal level unintentionally increases in the signal level which is the zero level or less. However, as shown in FIG. 6( a), there can be also the waveform distortion occurring on the optical disc 100 (or so-called low-to-high disc) in which the reflectance of the laser beam LB is increased by recording the data, as in an optical disc such as a Blu-ray disc in which a pigmented film is used as a recording layer. In other words, such waveform distortion can occur that the signal level unintentionally reduces in the signal level which is the zero level or more. Incidentally, in the case where such waveform distortion can occur that the signal level unintentionally reduces in the signal level which is the zero level or more, there can be such waveform distortion that the signal level in the front edge portion and the middle portion is changed, compared to the signal level in the rear edge portion of the read signal R_(RF), as shown in FIG. 6( b), as in the case where such waveform distortion occurs that the signal level unintentionally reduces as shown in FIG. 5( b), in the signal level which is the zero level or more. Moreover, there can be also such waveform distortion that the signal level in the middle portion and the rear edge portion is changed, compared to the signal level in the front edge portion of the read signal R_(RF), as shown in FIG. 6( c), as in the case where such waveform distortion occurs that the signal level unintentionally reduces shown in FIG. 5( c).

Moreover, in the example, it is preferable to focus on the waveform distortion which occurs in the read signal corresponding to the record mark with a relatively long run length (hereinafter referred to as a “long mark”: e.g. data with run lengths of 7 T to 11 T or 14 T if the optical disc 100 is a DVD, and data with run lengths of 6 T to 9 T if the optical disc 100 is a Blu-ray Disc). Alternatively, with emphasis on the importance of synchronization data (i.e. sync data), it is preferable to focus on the waveform distortion which occurs in the read signal corresponding to the mark corresponding to the synchronization data (e.g. data with a run length of 14 T if the optical disc 100 is a DVD, and data with a run length of 9 T if the optical disc 100 is a Blu-ray Disc).

(3) Operation Example of the Waveform Distortion Correction Circuit

Next, with reference to FIG. 7 to FIG. 9, an explanation will be given on a specific operation example of the waveform distortion correction circuit 18. FIG. 7 is a flowchart conceptually showing a flow of operations of the waveform distortion correction circuit 18. FIG. 8 is a block diagram conceptually showing the structure of the waveform distortion correction circuit 18. FIG. 9 is a waveform chart conceptually showing an operation of correcting the waveform distortion by the waveform distortion correction circuit 18, on the sample value series RS_(C).

As shown in FIG. 7, firstly, an operation of reproducing data recorded on the optical disc 100 is performed (step S101).

In the reproduction operation, by the operation of the reproduction property judgment circuit 20, it is judged or determined whether or not the read signal R_(RF) satisfies the desired reproduction property (in other words, whether or not the reproduction property of the read signal has a desired value) (step S102).

Specifically, it is sequentially judged whether or not a symbol error rate (SER) is less than or equal to a predetermined threshold value (e.g. approximately 0.001), or whether or not error correction using an ECC (Error Correction Code) or the like can be performed, or whether or not the synchronization data can be read. If it is judged that the symbol error rate is less than or equal to the threshold value (e.g. approximately 0.0001%), and that the error correction using the ECC or the like can be performed, and that the synchronization data can be read, it is judged that the read signal R_(RF) satisfies the desired reproduction property. On the other hand, if it is judged that the symbol error rate is not less than or equal to the threshold value (e.g. approximately 0.0001%), or that the error correction using the ECC or the like cannot be performed, or that the synchronization data cannot be read, it is judged that the read signal R_(RF) does not satisfy the desired reproduction property.

Incidentally, the predetermined threshold value which is a judgment criterion for the symbol error rate is preferably set on the basis of whether or not the preferable reproduction operation is performed. Specifically, it is preferable to set the value of the symbol error rate which does not allow the preferable reproduction operation as the predetermined threshold value.

As a result of the judgment in the step S102, if it is judged that the symbol error rate is less than or equal to the threshold value, and that the error correction can be performed, and that the synchronization data can be read (the step S102: Yes), the operational flow goes to a step S107.

On the other hand, as a result of the judgment in the step S102, if it is judged that the symbol error rate is not less than or equal to the threshold value, and that the error correction cannot be performed, and that the synchronization data cannot be read (the step S102: No), then, the waveform distortion of the long mark is measured (step S103). Here, a waveform distortion ratio (i.e. D/A×100) which indicates a ratio of the waveform distortion amount D (or D′) to the maximum amplitude A of the read signal R_(RF).

Then, it is judged whether or not the waveform distortion is greater than or equal to a predetermined value (step S104). For example, it is judged whether or not the waveform distortion ratio is greater than or equal to approximately 30%.

As a result of the judgment in the step S104, if it is judged that the waveform distortion is not greater than or equal to the predetermined value (e.g. that the waveform distortion ratio is less than or equal to approximately 30%) (the step S104: No), the operational flow goes to the step S107.

On the other hand, as a result of the judgment in the step S104, if it is judged that the waveform distortion is greater than or equal to the predetermined value (e.g. that the waveform distortion ratio is greater than or equal to approximately 30%) (the step S104: Yes), then, a waveform distortion correction condition, such as a correction level and a correction range for the waveform distortion, is set (step S105). The waveform distortion correction condition will be detailed later (refer to FIG. 9 and the like).

Then, the waveform distortion of the long mark is corrected on the basis of the waveform distortion correction condition set in the step S105 (step S106).

Then, it is judged whether or not the reproduction operation is to be ended (step S107), and if the reproduction operation is not to be ended (the step S107: No), the operational flow returns to the step S101, and the operations after the step S101 are repeated again.

The operation shown in FIG. 7 is performed mainly by the waveform distortion correction circuit 18. Now, the specific circuit structure of the waveform distortion correction circuit will be described.

As shown in FIG. 8, the waveform distortion correction circuit 18 is provided with a delay adjustment circuit 181, a distortion correction value detection circuit 182, a mark/space length detection circuit 183, a timing generation circuit 184, and a selector 185.

The read sample value series RS_(C) outputted from the pre-equalizer 14 is outputted to each of the delay adjustment circuit 181, the distortion correction value detection circuit 182, and the mark/space length detection circuit 183.

The distortion correction value detection circuit 182 holds a sample value S(k) at a time point which is a time corresponding to minT after the zero cross point and outputs it as a distortion correction value amd to the selector 185.

Moreover, the delay adjustment circuit 181 sets a delay amount corresponding to the longest run length of the record data and outputs the read sample value series RS_(C) to the selector 185 in desired timing. Specifically, if the optical disc 100 is a Blu-ray Disc, the delay adjustment circuit 181 sets a delay amount corresponding to the longest run length of 9 T, and if the optical disc 100 is a DVD, the delay adjustment circuit 181 sets a delay amount corresponding to the longest run length of 14 T.

Incidentally, minT indicates the read signal R_(RF) corresponding to the record data with the shortest run length (and more specifically the read sample value series RS_(C) corresponding to the read signal R_(RF)). For example, if the optical disc 100 is a DVD, the minT indicates the read signal R_(RF) corresponding to the record data with a run length of 3 T. For example, if the optical disc 100 is a Blu-ray Disc, the minT indicates the read signal R_(RF) corresponding to the record data with a run length of 2 T.

The mark/space length detection circuit 183 detects a mark/space length by detecting an interval between the zero cross points, the number of continuous coded bits, and the like. The detection result is outputted to the timing generation circuit 184.

The timing generation circuit 184 generates a timing signal SW on the basis of the mark/space length detected on the mark/space length detection circuit 183 and outputs the generated timing signal SW to the selector 185.

Specifically, the timing generation circuit 184 generates a high-level timing signal SW (SW=1) (i) if the mark/space length detected on the mark/space length detection circuit 183 is the long mark which is a target of the waveform distortion correction and (ii) in a period between a time point T1 which is at least a time corresponding to the minT after a first zero cross point and a time point T2 which is the time corresponding to the minT before a second zero cross point located next to the first zero cross point, and the timing generation circuit 184 outputs the generated timing signal SW to the selector 185. On the other hand, the timing generation circuit 184 generates a low-level timing signal SW (SW=0) (i) if the mark/space length detected on the mark/space length detection circuit 183 is a mark other than the long mark which is a target of the waveform distortion correction or (ii) in a period other than the period between the time point T1 which is at least a time corresponding to the minT after the first zero cross point and the time point T2 which is the time corresponding to the minT before the second zero cross point located next to the first zero cross point, and the timing generation circuit 184 outputs the generated timing signal SW to the selector 185.

If the high-level timing signal SW is outputted from the timing generation circuit 184, the selector 185 outputs the distortion correction value amd outputted from the distortion correction value detection circuit 182, to the limit equalizer 15 as the distortion-corrected read sample value series RS_(CAM). On the other hand, if the low-level timing signal SW is outputted from the timing generation circuit 184, the selector 185 outputs the read sample value series RS_(C) outputted from the delay adjustment circuit 181, to the limit equalizer 15 as the distortion-corrected read sample value series RS_(CAM).

Incidentally, the waveform distortion correction condition set in the step S105 in FIG. 7 substantially corresponds to the distortion correction value amd detected on the distortion correction value detection circuit 182 and the timing signal SW generated on the timing generation circuit 184.

The operations by the waveform distortion correction circuit 18 will be described more clearly on a waveform chart showing the sample value series RS_(C).

As shown in FIG. 9, in the period between the time point T1 which is at least the time corresponding to the minT after the first zero cross point and the time point T2 which is the time corresponding to the minT before the second zero cross point located next to the first zero cross point (i.e. in the period in which the timing signal SW is at high level), sample values included in the sample value series RS_(C) are corrected to the distortion correction value amd detected on the distortion correction value detection circuit 182. As a result, the waveform distortion is corrected.

An effect obtained by correcting the waveform distortion will be described with reference to FIG. 10 to FIG. 12. FIG. 10 is a waveform chart conceptually showing a waveform or the like of the read signal R_(RF) before and after the correction of the waveform distortion. FIG. 11 are waveform charts conceptually showing the operation of obtaining the high-frequency emphasized read sample value series RS_(H), on the sample value series RS_(C), in each of a case where the waveform distortion is not corrected and a case where the waveform distortion is corrected. FIG. 12 is a graph showing a change in symbol error rate with respect to the waveform distortion ratio.

As shown on the left side of FIG. 10, if the waveform distortion occurs in the read signal R_(RF), the waveform distortion is likely misjudged to be the normal mark (e.g. the mark with a relatively short run length). Therefore, the binary waveform after binarizing the read signal R_(RF) includes an error signal caused by the waveform distortion. This results in inconsistency with the original record data and causes a binary error.

On the other hand, as shown on the right side of FIG. 10, if the waveform distortion occurring in the read signal R_(RF) is corrected, the binary waveform after binarizing the read signal R_(RF) no longer includes the error signal caused by the waveform distortion. This results in consistency with the original record data and does not cause the binary error.

More specifically explaining this, depending on a condition such as the magnitude of the waveform distortion, as shown in FIG. 11( a), the waveform distortion likely has a signal level which is greater than the lower limit −L of the amplitude limit value on the limit equalizer 15. In this case, the high-frequency emphasized read sample value series RS_(H) outputted from the high-frequency emphasis block 153 is the sum of a high-frequency emphasized read sample value series RS_(HIG) and S(0), and as described above, RS_(HIG)=(−k)×Sip(−1)+k×Sip(0)+k×Sip(1)+(−k)×Sip(2). Here, since Sip(−1) and Sip(2) are limited by the lower limit −L, RS_(H)=S(0)+k×(−2×−L+Sip(0)+Sip(1)). This increases the value of the high-frequency emphasized read sample value series RS_(H), by the value obtained by multiplying the sum of the lower limit −L, Sip(0), and Sip(1) by K. This is not preferable because it emphasizes the waveform distortion which is originally not to occur. Moreover, for example, the emphasized waveform distortion likely leads to such a disadvantage that the mark with a relatively long run length in which the waveform distortion occurs is misjudged to be another mark in an information reproducing apparatus which adopts the PRML. This results in the binary error.

Moreover, this is not illustrated, but in the same manner, in the optical disc 100 in which the reflectance of the laser beam LB is reduced by forming the marks shown in FIG. 6( a) to FIG. 6( c), Sip(−1) and Sip(2) are limited by the upper limit L, so that RS_(H)=S(0)+k×(−2×L+Sip(0)+Sip(1)). This increases the value of the high-frequency emphasized read sample value series RS_(H), by the value obtained by multiplying the sum of the upper limit L, Sip(0), and Sip(1) by K. This is not preferable because it emphasizes the waveform distortion which is originally not to occur.

On the other hand, as shown in FIG. 11( b), if the waveform distortion is corrected, the signal level of the waveform distortion can be corrected to be a signal level which is less than or equal to the lower limit −L of the amplitude limit value on the limit equalizer 15. In this case, Sip(−1) and Sip(0), and Sip(1) and Sip(2) are limited by the lower limit −L, so that RS_(H)=S(0). Thus, it is possible to prevent such a disadvantage that the waveform distortion is emphasized, and as a result, it is possible to prevent such a disadvantage that the binary error occurs.

Moreover, this is not illustrated, but in the same manner, in the optical disc 100 in which the reflectance of the laser beam LB is reduced by forming the marks shown in FIG. 6( a) to FIG. 6( c), if the waveform distortion is corrected, Sip(−1) and Sip(0), and Sip(1) and Sip(2) are limited by the upper limit L, so that RS_(H)=S(0). Thus, it is possible to prevent such a disadvantage that the waveform distortion is emphasized, and as a result, it is possible to prevent such a disadvantage that the binary error occurs.

As described above, the effect by correcting the waveform distortion can be also seen from a change in symbol error rate with respect to the waveform distortion ratio. As shown in FIG. 12, the value of SER in the case where the waveform distortion is corrected is improved, compared to the value of SER in the case where the waveform distortion is not corrected.

As explained above, according to the information reproducing apparatus 1 in the example, the dispersion of the sample values before and after the reference sample point is forcibly controlled in the read signal which causes the intersymbol interference in the high-frequency emphasis. Thus, even if the sufficient high-frequency emphasis is performed on the high-frequency emphasis block 153, the intersymbol interference does not occur.

In particular, according to the information reproducing apparatus 1 in the example, the amplitude limit and the high-frequency emphasis are performed on the limit equalizer 15 after the waveform distortion is corrected. Thus, it is possible to preferably prevent such a disadvantage that the waveform distortion which is originally not to occur is emphasized on the limit equalizer 15. Moreover, it is possible to preferably prevent such a disadvantage that the mark with a relatively long run length is misjudged to be another mark, in the information reproducing apparatus which adopts the PRML for example due to the emphasized waveform distortion. As a result, the waveform distortion rarely causes the binary error, and this allows the preferable reproduction operation.

In addition, the waveform distortion is selectively corrected by the waveform distortion correction circuit 18 when it is judged by the reproduction property judgment circuit 20 that the read signal R_(RF) does not satisfy the desired reproduction property. Here, in particular, as opposed to the optical disc 100 which allows only sequential recording, various recording statuses are mixed in the optical disc 100 which allows random recording. In this case, it is necessary to read the read signal R_(RF) in which the waveform distortion is discontinuously or discretely distributed or not distributed, or to read the read signal R_(RF) which has various signal levels. Therefore, by reproducing the record data without correcting the waveform distortion in a normal case, and by reproducing the record data while selectively correcting the waveform distortion in the case where the read signal R_(RF) does not satisfy the desired reproduction property (i.e. where the waveform distortion highly likely occurs), it is possible to receive the aforementioned various effects while reducing the load of the information reproducing apparatus 1.

Incidentally, if the SER is used as the reproduction property of the read signal R_(RF), the aforementioned decoding circuit 17 preferably performs an error correction process in addition to the decoding process. Namely, if the SER is used as the reproduction property of the read signal R_(RF), the aforementioned decoding circuit 17 is preferably a decoding/correction circuit 17.

(2) First Modified Example

Next, with reference to FIG. 13 to FIG. 15, a first modified example of the information reproducing apparatus 1 in the example will be described. FIG. 13 is a block diagram conceptually showing the structure of a waveform distortion correction circuit 18 a provided for an information reproducing apparatus 1 a in the first modified example. FIG. 14 is a block diagram conceptually showing the structure of a waveform distortion detection circuit 186 a provided for the waveform distortion correction circuit 18 a provided for the information reproducing apparatus 1 a in the first modified example. FIG. 15 is a flowchart conceptually showing a flow of operations of the information reproducing apparatus 1 a in the first modified example.

In the operation example shown in FIG. 7, the waveform distortion is always corrected when the read signal R_(RF) does not satisfy the desired reproduction property. In the first modified example, however, even if read signal R_(RF) does not satisfy the desired reproduction property, the waveform distortion is corrected selectively when the waveform distortion is actually detected. Hereinafter, the specific structure and operation example of the first modified example will be described.

As shown in FIG. 13, the waveform distortion correction circuit 18 a is provided with the delay adjustment circuit 181, a waveform distortion detection circuit 186 a, the mark/space length detection circuit 183, the timing generation circuit 184, the selector 185, and an AND circuit 187 a.

In this aspect, a result of the detection of the mark/space length by the mark/space length detection circuit 183 is outputted to the waveform distortion detection circuit 186 a, in addition to the timing generation circuit 184.

The waveform distortion detection circuit 186 a detects the waveform distortion and outputs a waveform distortion detection signal DT which indicates that the waveform distortion is detected, to the AND circuit 187 a. More specifically, the waveform distortion detection circuit 186 a outputs a high-level waveform distortion detection signal DT (DT=1) to the AND circuit 187 a if the waveform distortion is detected, and outputs a low-level waveform distortion detection signal DT (DT=0) to the AND circuit 187 a if the waveform distortion is not detected.

The AND circuit 187 a generates a high-level timing signal SWO if the waveform distortion is detected (if each of the timing signal SW outputted from the timing generation circuit 184 and the waveform distortion detection signal DT outputted from the waveform distortion detection circuit 186 a is high-level), on the basis of the output of each of the timing generation circuit 184 and the waveform distortion detection circuit 186 a. On the other hand, the AND circuit 187 a generates a low-level timing signal SW0 if the waveform distortion is not detected (if either the timing signal SW outputted from the timing generation circuit 184 or the waveform distortion detection signal DT outputted from the waveform distortion detection circuit 186 a is low-level), on the basis of the output of each of the timing generation circuit 184 and the waveform distortion detection circuit 186 a. In other words, in the first modified example, the waveform distortion is corrected selectively when the waveform distortion is detected.

As shown in FIG. 14, the waveform distortion detection circuit 186 a is provided with a shift register 1831 a, a selector 1832 a, a maximum value detection circuit 1833 a, a minimum value detection circuit 1834 a, a subtracter 1835 a, and a judgment circuit 1836 a.

The read sample value series RS_(C) inputted to the waveform distortion detection circuit 186 a is outputted to the shift register 1831 a. The shift register 1831 a outputs the inputted read sample value series RS_(C) to the selector 1832 a as outputs D0 to D14 while shifting the inputted read sample value series RS_(C) by one clock.

The selector 1832 a selectively samples and holds three outputs from among the outputs D0 to D14, on the basis of the mark/space length, in timing outputted from the mark/space length detection circuit 183, and outputs the three outputs to a distortion correction amount detection circuit 1837 a, the maximum value detection circuit 1833 a, and the minimum value detection circuit 1834 a, respectively.

More specifically, the selector 1832 a selectively samples and holds three outputs D2, D3, and D4 from among the outputs D0 to D14 if the mark/space length outputted from the mark/space length detection circuit 183 is 6 T, and outputs the three outputs to the distortion correction amount detection circuit 1837 a, the maximum value detection circuit 1833 a, and the minimum value detection circuit 1834 a, respectively. The selector 1832 a selectively samples and holds three outputs D2, D3, and D5 from among the outputs D0 to D14 if the mark/space length outputted from the mark/space length detection circuit 183 is 7 T, and outputs the three outputs to the distortion correction amount detection circuit 1837 a, the maximum value detection circuit 1833 a, and the minimum value detection circuit 1834 a, respectively. The selector 1832 a selectively samples and holds three outputs D2, D4, and D6 from among the outputs D0 to D14 if the mark/space length outputted from the mark/space length detection circuit 183 is 8 T, and outputs the three outputs to the distortion correction amount detection circuit 1837 a, the maximum value detection circuit 1833 a, and the minimum value detection circuit 1834 a, respectively. The selector 1832 a selectively samples and holds three outputs D2, D4, and D7 from among the outputs D0 to D14 if the mark/space length outputted from the mark/space length detection circuit 183 is 9 T, and outputs the three outputs to the distortion correction amount detection circuit 1837 a, the maximum value detection circuit 1833 a, and the minimum value detection circuit 1834 a, respectively. The selector 1832 a selectively samples and holds three outputs D2, D5, and D8 from among the outputs D0 to D14 if the mark/space length outputted from the mark/space length detection circuit 183 is 10 T, and outputs the three outputs to the distortion correction amount detection circuit 1837 a, the maximum value detection circuit 1833 a, and the minimum value detection circuit 1834 a, respectively. The selector 1832 a selectively samples and holds three outputs D2, D5, and D9 from among the outputs D0 to D14 if the mark/space length outputted from the mark/space length detection circuit 183 is 11 T, and outputs the three outputs to the distortion correction amount detection circuit 1837 a, the maximum value detection circuit 1833 a, and the minimum value detection circuit 1834 a, respectively. The selector 1832 a selectively samples and holds three outputs D2, D7, and D12 from among the outputs D0 to D14 if the mark/space length outputted from the mark/space length detection circuit 183 is 14 T, and outputs the three outputs to the distortion correction amount detection circuit 1837 a, the maximum value detection circuit 1833 a, and the minimum value detection circuit 1834 a, respectively. The operation of the selector 1832 a described above substantially corresponds to the operation of selectively outputting the signal level in the front edge portion, the signal level in the middle portion, and the signal level in the rear edge portion of the waveform distortion, shown in FIG. 5( a) to FIG. 5( c) and FIG. 6( a) to FIG. 6( c).

Then, on the distortion correction amount detection circuit 1837 a, desired one signal level of the three outputs outputted from the selector 1832 a (i.e. the signal level in the front edge portion, the signal level in the middle portion, and the signal level in the rear edge portion) is outputted as the distortion correction value amd. Specifically, as shown in FIG. 5( a) and FIG. 6( a), for the waveform distortion in which the signal level in the middle portion is changed, for example, the signal level in the front edge portion or the signal level in the rear edge portion is outputted as the distortion correction value amd. As shown in FIG. 5( b) and FIG. 6( b), for the waveform distortion in which the signal level in the front edge portion is changed, for example, the signal level in the rear edge portion is outputted as the distortion correction value amd. As shown in FIG. 5( c) and FIG. 6( c), for the waveform distortion in which the signal level in the rear edge portion is changed, for example, the signal level in the front edge portion is outputted as the distortion correction value amd.

Moreover, on the maximum value detection circuit 1833 a, the maximum value (i.e. the maximum signal level) of the three outputs outputted from the selector 1832 a is detected, and the detected maximum value is outputted to the subtracter 1835 a.

Moreover, on the minimum value detection circuit 1834 a, the minimum value (i.e. the minimum signal level) of the three outputs outputted from the selector 1832 a is detected, and the detected minimum value is outputted to the subtracter 1835 a.

Then, on the subtracter 1835 a, the minimum value detected on the minimum value detection circuit 1834 a is subtracted from the maximum value detected on the maximum value detection circuit 1833 a, by which the waveform distortion amount D is calculated.

Then, on the judgment circuit 1836 a, it is judged whether or not the waveform distortion amount outputted from the subtracter 1835 a is greater than or equal to a predetermined value x. If the waveform distortion amount D is relatively small, the waveform distortion is not regarded as being detected, and the low-level waveform distortion detection signal DT is outputted. On the other hand, if the waveform distortion amount D is relatively large (e.g. if the waveform distortion ratio is greater than or equal to approximately 30%), the waveform distortion is regarded as being detected, and the high-level waveform distortion detection signal DT is outputted. In a flow of the operations at this time, as shown in FIG. 15, firstly, an operation of reproducing data recorded on the optical disc 100 is performed (step S101). In the reproduction operation, it is judged whether or not the read signal R_(RF) satisfies the desired reproduction property (step S102).

As a result of the judgment in the step S102, if it is judged that the read signal R_(RF) satisfies the desired reproduction property (the step S102: Yes), the operational flow goes to a step S107.

On the other hand, as a result of the judgment in the step S102, if it is judged that the read signal R_(RF) does not satisfy the desired reproduction property (the step S102: No), then, it is judged whether or not the waveform distortion is actually detected on the waveform distortion detection circuit 186 a (step S201).

As a result of the judgment in the step S201, if it is judged that the waveform distortion is not detected (the step S201: No), the operational flow goes to the step S107 without correcting the waveform distortion (i.e. without performing the operations in the step S103 to the step S106).

On the other hand, as a result of the judgment in the step S201, if it is judged that the waveform distortion is detected (the step S201: Yes), the operational flow goes to the step S107 after correcting the waveform distortion (i.e. after performing the operations in the step S103 to the step S106).

As described above, by selectively correcting the waveform distortion when the waveform distortion is detected, it is possible to receive the aforementioned various effects while reducing the load of the information reproducing apparatus 1 a.

In addition, the waveform distortion is selectively corrected by the waveform distortion correction circuit 18 when the waveform distortion actually occurs. Here, in particular, as opposed to the optical disc 100 which allows only sequential recording, various recording statuses are mixed in the optical disc 100 which allows random recording. In this case, it is necessary to read the read signal R_(RF) in which the waveform distortion is discontinuously or discretely distributed or not distributed, or to read the read signal R_(RF) which has various signal levels. Therefore, by reproducing the record data without correcting the waveform distortion in a normal case, and by reproducing the record data while selectively correcting the waveform distortion in the case where the waveform distortion actually occurs, it is possible to receive the aforementioned various effects while reducing the load of the information reproducing apparatus 1.

In addition, according to the information reproducing apparatus 1 a in the first modified example, the signal level of the waveform distortion can be corrected to desired one of the signal level in the front edge portion, the signal level in the middle portion, and the signal level in the rear edge portion. Thus, it is possible to preferably correct the waveform distortion in various shapes. Specifically, in the construction explained with reference to FIG. 7 to FIG. 9, the signal level of the waveform distortion is corrected to the signal level in the front edge portion. Thus, particularly, the waveform distortion in which the signal level in the front edge portion is changed, as shown in FIG. 5(b) and FIG. 6( b), cannot be preferably corrected. According to the information reproducing apparatus 1 a in the first modified example, however, this type of waveform distortion can be preferably corrected.

(3) Second Modified Example

Next, with reference to FIG. 16, a second modified example of the information reproducing apparatus 1 in the example will be described. FIG. 16 is a flowchart conceptually showing a flow of operations of an information reproducing apparatus 1 b in the second modified example.

Incidentally, in the operation example shown in FIG. 7, only one waveform distortion correction condition is set; however, in the second modified example, a plurality of waveform distortion correction conditions are set, and the waveform distortion correction is performed by applying the waveform distortion correction conditions in order.

In a flow the operations at this time, as shown in FIG. 16, firstly, the operation of reproducing data recorded on the optical disc 100 is performed (step S101). In the reproduction operation, it is judged whether or not the read signal R_(RF) satisfies the desired reproduction property (step S102).

As a result of the judgment in the step S102, if it is judged that the read signal R_(RF) satisfies the desired reproduction property (the step S102: Yes), the operational flow goes to a step S107.

On the other hand, as a result of the judgment in the step S102, if it is judged that the read signal R_(RF) does not satisfy the desired reproduction property (the step S102: No), then, it is judged whether or not the waveform distortion is actually detected on the waveform distortion detection circuit 186 a (step S201).

As a result of the judgment in the step S201, if it is judged that the waveform distortion is not detected (the step S201: No), the operational flow goes to the step S107 without correcting the waveform distortion (i.e. without performing the operations in the step S103 to the step S106).

On the other hand, as a result of the judgment in the step S201, if it is judged that the waveform distortion is detected (the step S201: Yes), the waveform distortion of the long mark is measured (step S103). Then, it is judged whether or not the waveform distortion is greater than or equal to a predetermined value (step S104).

As a result of the judgment in the step S104, if it is judged that the waveform distortion is not greater than or equal to the predetermined value (e.g. that the waveform distortion ratio is less than or equal to approximately 30%) (the step S104: No), the operational flow goes to the step S107.

On the other hand, as a result of the judgment in the step S104, if it is judged that the waveform distortion is greater than or equal to the predetermined value (e.g. that the waveform distortion ratio is greater than or equal to approximately 30%) (the step S104: Yes), then, a waveform distortion correction condition #x (wherein x is an integer of 1 or more, with an initial value of 1), such as a correction level and a correction range for the waveform distortion, is set (step S301). Then, on the basis of the waveform distortion correction condition #x set in the step S301, the waveform distortion of the long mark is corrected (step S106).

Then, it is judged whether or not the retry number is greater than or equal to a predetermined value, wherein the retry number is the number of times to correct the waveform distortion (step S302).

As a result of the judgment in the step S302, if it is judged that the retry number is not greater than or equal to the predetermined value (the step S302: No), x is incremented by 1. Then, the operational flow returns to the step S102, and the operations after the step S102 are repeated; namely, the correction of the waveform distortion is repeated (in other words, retried) while changing the waveform distortion correction condition as occasion demands.

On the other hand, as a result of the judgment in the step S302, if it is judged that the retry number is greater than or equal to the predetermined value (the step S302: Yes), the operational flow goes to the step S107.

Incidentally, as the plurality of waveform distortion correction conditions, it is preferable to use the waveform distortion correction conditions used in the operations in modified examples detailed later with reference to FIG. 22 to FIG. 45.

(3) Third Modified Example

Next, with reference to FIG. 17 to FIG. 21, an information reproducing apparatus 1 c in a third modified example will be described. FIG. 17 is a timing chart conceptually showing an operation of correcting the waveform distortion by a waveform distortion correction circuit 18 c provided for the information reproducing apparatus 1 c in the third modified example, on a first read signal R_(RF). FIG. 18 is a timing chart conceptually showing the operation of correcting the waveform distortion by the waveform distortion correction circuit 18 c provided for an information reproducing apparatus 1 c in the third modified example, on a second read signal R_(RF). FIG. 19 is a flowchart conceptually showing a first flow of operations by the waveform distortion correction circuit 18 c provided for the information reproducing apparatus 1 e in the third modified example. FIG. 20 is a flowchart conceptually showing a second flow of operations by the waveform distortion correction circuit 18 c provided for the information reproducing apparatus 1 c in the third modified example. FIG. 21 is a flowchart conceptually showing a third flow of operations by the waveform distortion correction circuit provided for the information reproducing apparatus 1 c in the third modified example.

The record data recorded on the optical disc 100 includes not only normal user data but also the synchronization data (e.g. the record data with a run length of 14 T if the optical disc 100 is a DVD, and the record data with a run length of 9 T if the optical disc 100 is a Blu-ray Disc) used for synchronization in reproducing the user data. In the third modified example, considering that the synchronization data is included in the record data, the correction of the waveform distortion may be limited to the synchronization data.

More specifically, as shown in FIG. 17, if the optical disc 100 is a Blu-ray Disc, since the synchronization data is formed of a 9 T mark and a 9 T space, firstly, the 9 T space is detected, and the waveform distortion before or after the detected 9 T space may be corrected. Moreover, focusing on periodicity that the synchronization data appears, the waveform distortion may be corrected near a position being shifted by a time corresponding to 1932 T (or 1932 T±α1: α1 is a predetermined constant) from the detected 9 T space toward the advancing direction (or a position being shifted by β1 T from the relevant position toward the advancing direction: β1 is a predetermined constant).

Moreover, as shown in FIG. 18, if the optical disc 100 is a DVD, since the synchronization data is a 14 T mark or a 14 T space, firstly, the 14 T space is detected, and the waveform distortion may be corrected near a position being shifted by a time corresponding to 1488 T (or 1488 T±α2: α2 is a predetermined constant) from the detected 14 T space toward the advancing direction (or a position being shifted by β2 T from the relevant position toward the advancing direction: β2 is a predetermined constant).

A flow of the operations if the optical disc 100 is a Blu-ray Disc (a first operational flow) will be described, with reference to FIG. 19.

As shown in FIG. 19, firstly, the operation of reproducing data recorded on the optical disc 100 is performed (step S101).

In the reproduction operation, it is judged whether or not the 9 T space is detected (step S401).

As a result of the judgment in the step S401, if it is judged that the 9 T space is not detected (the step S401: No), the operational flow returns to the step S401 again, and the judgment operation of whether or not the 9 T space is detected is repeated.

On the other hand, as a result of the judgment in the step S401, if it is judged that the 9 T space is detected (the step S401: Yes), then, it is judged whether or not the record data (in other words, the read signal R_(RF)) immediately before or immediately after the 9 T space is the 9 T mark (step S402).

As a result of the judgment in the step S402, if it is judged that the record data immediately before or immediately after the 9 T space is the 9 T mark (the step S402: Yes), the operations are ended without change.

On the other hand, as a result of the judgment in the step S402, if it is judged that the record data immediately before or immediately after the 9 T space is not the 9 T mark (the step S402: No), the waveform distortion immediately before or immediately after the 9 T space or near the both positions is corrected (step S404). The correction of the waveform distortion in the step S404 is performed in the same manner as the operations in the step S103 to the step 106 in FIG. 7 or the operations in the step S201 to the step S106 in FIG. 15.

Next, another flow of the operations if the optical disc 100 is a Blu-ray Disc (a second operational flow) will be described, with reference to FIG. 20.

As shown in FIG. 20, firstly, the operation of reproducing data recorded on the optical disc 100 is performed (step S101).

In the reproduction operation, it is judged whether or not the 9 T space is detected (step S401).

As a result of the judgment in the step S401, if it is judged that the 9 T space is not detected (the step S401: No), the operational flow returns to the step S401 again, and the judgment operation of whether or not the 9 T space is detected is repeated.

On the other hand, as a result of the judgment in the step S401, if it is judged that the 9 T space is detected (the step S401: Yes), then, it is judged whether or not the record data at a position being shifted by a time corresponding to 1932 T (or 1932±α1) from the detected 9 T space toward the advancing direction (or a position being shifted by β1 T from the relevant position toward the advancing direction) is the 9 T mark (step S502).

As a result of the judgment in the step S502, if it is judged that the record data at the position being shifted by the time corresponding to 1932 T (or 1932±α1) from the detected 9 T space toward the advancing direction (or the position being shifted by β1 T from the relevant position) is the 9 T mark (the step S502: Yes), the operations are ended without change.

On the other hand, as a result of the judgment in the step S502, if it is judged that the record data at the position being shifted by the time corresponding to 1932 T (or 1932±α1) from the detected 9 T space toward the advancing direction (or the position being shifted by β1 T from the relevant position toward the advancing direction) is not the 9 T mark (the step S502: No), the waveform distortion is corrected near the position being shifted by the time corresponding to 1932 T (or 1932±α1) from the detected 9 T space toward the advancing direction (or the position being shifted by β1 T from the relevant position toward the advancing direction) (step S504). The correction of the waveform distortion in the step S504 is performed in the same manner as the operations in the step S103 to the step 106 in FIG. 7 or the operations in the step S201 to the step S106 in FIG. 15.

Next, a flow of the operations if the optical disc 100 is a DVD (a third operational flow) will be described, with reference to FIG. 21.

As shown in FIG. 21, firstly, the operation of reproducing data recorded on the optical disc 100 is performed (step S101).

In the reproduction operation, it is judged whether or not the 14 T space is detected (step S601).

As a result of the judgment in the step S601, if it is judged that the 14 T space is not detected (the step S601: No), the operational flow returns to the step S601 again, and the judgment operation of whether or not the 14 T space is detected is repeated.

On the other hand, as a result of the judgment in the step S601, if it is judged that the 14 T space is detected (the step S601: Yes), then, it is judged whether or not the read signal R_(RF) at a position being shifted by a time corresponding to 1488 T (or 1488±α2) from the detected 14 T space toward the advancing direction (or a position being shifted by β2 T from the relevant position toward the advancing direction) is the 14 T mark or the 14 T space (step S602).

As a result of the judgment in the step S602, if it is judged that the read signal R_(RF) at the position being shifted by the time corresponding to 1488 T (or 1488±α2) from the detected 14 T space toward the advancing direction (or a position being shifted by β2 T from the relevant position toward the advancing direction) is the 14 T mark or the 14 T space (the step S602: Yes), the operations are ended without change.

On the other hand, as a result of the judgment in the step S602, if it is judged that the read signal R_(RF) at the position being shifted by the time corresponding to 1488 T (or 1488±α2) from the detected 14 T space toward the advancing direction (or a position being shifted by 2 T from the relevant position toward the advancing direction) is not the 14 T mark or the 14 T space (the step 8602: No), the waveform distortion is corrected near the position being shifted by the time corresponding to 1488 T (or 1488±α2) from the detected 14 T space toward the advancing direction (or a position being shifted by β2 T from the relevant position toward the advancing direction) (step S604). The correction of the waveform distortion in the step S604 is performed in the same manner as the operations in the step S103 to the step 106 in FIG. 7 or the operations in the step S201 to the step S106 in FIG. 15.

As described above, by correcting the waveform distortion in view of that the synchronization data is included in the record data, it is possible to preferably perform the high-frequency emphasis on the synchronization data which is more important than the user data, resulting in the preferable reproduction of the synchronization data. This can further increase the stability of the reproduction operation.

(5) Fourth Modified Example Another Example of Waveform Distortion Correction Value amd

Next, with reference to FIG. 22 and FIG. 23, an information reproducing apparatus 1 d in a fourth modified example will be described. FIG. 22 is a waveform chart conceptually showing an operation of correcting the waveform distortion by a waveform distortion correction circuit 18 d provided for the information reproducing apparatus 1 d in the fourth modified example, on the sample value series RS_(C). FIG. 23 is a block diagram conceptually showing the structure of the waveform distortion correction circuit 18 d provided for the information reproducing apparatus 1 d in the fourth modified example.

Incidentally, the same structures and operations as those in the aforementioned example carry the same reference numerals, and the explanation thereof is omitted.

As shown in FIG. 22, in the fourth modified example, as the distortion correction value amd, the average value of center samples of a mark with a run length of (min+3)T (i.e. the minimum amplitude value of the mark with (min+3)T for the waveform distortion shown in FIG. 5( a) to FIG. 5( c), and the maximum amplitude value of the mark with (min+3)T for the waveform distortion shown in FIG. 6( a) to FIG. 6( c)) is used.

Incidentally, (min+k)T indicates the read signal R_(RF) (and more specifically, the read sample value series RS_(C) corresponding to the read signal R_(RF)) corresponding to the record data with the (k+1)th shortest run length (wherein k is an integer or 1 or more). Therefore, (min+3)T indicates the read signal R_(RF) (and more specifically, the read sample value series RS_(C) corresponding to the read signal R_(RF)) corresponding to the record data with the fourth shortest run length. For example, if the optical disc 100 is a DVD, (min+3)T indicates the read signal R_(RF) corresponding to the record data with a run length of 6 T. For example, if the optical disc 100 is a Blu-ray Disc, (min+3)T indicates the read signal R_(RF) corresponding to the record data with a run length of 5 T.

In this case, as shown in FIG. 23, the waveform distortion correction circuit 18 d is provided with the delay adjustment circuit 181, a distortion correction value detection circuit 182 d, the mark/space length detection circuit 183, the timing generation circuit 184, and the selector 185.

The distortion correction value detection circuit 182 d holds and averages the center sample values of the record data if the record data with a run length of (min+3)T is inputted, while monitoring the mark/space length outputted from the mark/space length detection circuit 183, and outputs it to the selector 185 as the distortion correction value.

As described above, even if the average value of the center samples of the record data with a run length of (min+3)T is used as the distortion correction value amd, it is possible to preferably receive the aforementioned various effects.

Moreover, depending on circumstances, by correcting the waveform distortion, the signal level after the correction is increased from the original signal level (i.e. the signal level before the correction). Thus, by correcting the waveform distortion, it is possible to bring the signal level closer to the maximum amplitude of the read signal R_(RF). As a result, particularly in the information reproducing apparatus which adopts the PRML (Partial Response Maximum Likelihood), the record data can be reproduced more preferably.

Incidentally, as the distortion correction value amd, instead of the average value of the center samples of the record data with a run length of (min+3)T, the average value of the center samples of the record data with another run length may be used. In this case, as the record data with another run length, the record data which can realize the maximum amplitude is preferably used.

(6) Fifth Modified Example Another Example of Waveform Distortion Correction Value amd

Next, with reference to FIG. 24 and FIG. 25, an information reproducing apparatus 1 e in a fifth modified example will be described. FIG. 24 is a waveform chart conceptually showing an operation of correcting the waveform distortion by a waveform distortion correction circuit 18 e provided for the information reproducing apparatus 1 e in the fifth modified example, on the sample value series RS_(C). FIG. 25 is a block diagram conceptually showing the structure of the waveform distortion correction circuit 18 e provided for the information reproducing apparatus 1 e in the fifth modified example.

Incidentally, the same structures and operations as those in the aforementioned example carry the same reference numerals, and the explanation thereof is omitted.

As shown in FIG. 24, in the fifth modified example, as the distortion correction value amd, the maximum value or minimum value of a digital code for indicating the read sample value series RS_(H) (i.e. the minimum value of the digital code for the waveform distortion shown in FIG. 5( a) to FIG. 5( c), and the minimum value of the digital code for the waveform distortion shown in FIG. 6( a) to FIG. 6( c)) is used. For example, if the digital code is 8-bit, the maximum value of the digital code is 2̂(8−1)−1=127, and the minimum value of the digital code is −2̂(8−1)−1=−128.

In this case, as shown in FIG. 25, the waveform distortion correction circuit 18 e is provided with the delay adjustment circuit 181, a distortion correction value detection circuit 182 e, the mark/space length detection circuit 183, the timing generation circuit 184, and the selector 185.

The distortion correction value detection circuit 182 e outputs the maximum value or minimum value of the digital code, to the selector 185 as the distortion correction value.

As described above, even if the maximum value or minimum value of the digital code is used as the distortion correction value amd, it is possible to preferably receive the aforementioned various effects.

In addition, it is no longer necessary to sequentially detect the distortion correction value amd, so that it is possible to relatively reduce a load of the waveform distortion correction circuit 18 e (i.e. a load of the information reproducing apparatus 1 e).

Incidentally, if not only the maximum value or minimum value of the digital code but also a predetermined fixed value is used as the distortion correction value amd, it is possible to preferably receive the aforementioned various effects while relatively reducing the load of the waveform distortion correction circuit 18 e (i.e. the load of the information reproducing apparatus 1 e).

(7) Sixth Modified Example Another Example of Waveform Distortion Correction Value amd

Next, with reference to FIG. 26 and FIG. 27, an information reproducing apparatus if in a sixth modified example will be described. FIG. 26 is a waveform chart conceptually showing an operation of correcting the waveform distortion by a waveform distortion correction circuit 18 f provided for the information reproducing apparatus 1 f in the sixth modified example, on the sample value series RS_(C). FIG. 27 is a block diagram conceptually showing the structure of the waveform distortion correction circuit 18 f provided for the information reproducing apparatus 1 f in the sixth modified example.

Incidentally, the same structures and operations as those in the aforementioned example carry the same reference numerals, and the explanation thereof is omitted.

As shown in FIG. 26, in the sixth modified example, as the distortion correction value amd, the upper limit L or lower limit −L of the amplitude limit value on the limit equalizer 15 (i.e. the lower limit −L of the amplitude limit value for the waveform distortion shown in FIG. 5( a) to FIG. 5( c), and the upper limit L of the amplitude limit value for the waveform distortion shown in FIG. 6( a) to FIG. 6( c)) is used.

In this case, as shown in FIG. 27, the waveform distortion correction circuit 18 f is provided with the delay adjustment circuit 181, the mark/space length detection circuit 183, the timing generation circuit 184, and the selector 185.

The selector 185 outputs the upper limit L or lower limit −L of the amplitude limit value on the limit equalizer 15 as the distortion correction sample value series RS_(CAM) if the high-level timing signal SW is outputted from the timing generation circuit 184.

As described above, even if the upper limit L or lower limit −L of the amplitude limit value on the limit equalizer 15 is used as the distortion correction value amd, it is possible to preferably receive the aforementioned various effects.

In addition, since the signal level of the waveform distortion is corrected to the upper limit L or lower limit −L of the amplitude limit value on the limit equalizer 15, it is certainly possible to prevent such a disadvantage that the waveform distortion which is originally not to occur is emphasized. Moreover, it is also possible to preferably prevent such a disadvantage that the mark with a relatively long run length is misjudged to be another mark, caused by the emphasized waveform distortion, in the information reproducing apparatus which adopts the PRML. As a result, the binary error caused by the waveform distortion hardly occurs, which allows the preferable reproduction operation.

Incidentally, a value which is greater than or equal to the upper limit L or a value which is less than or equal to the lower limit −L of the amplitude limit value on the limit equalizer 15 may be used. Even in such construction, it is possible to preferably receive the aforementioned various effects.

(8) Seventh Modified Example Another Example of Waveform Distortion Correction Value amd

Next, with reference to FIG. 28 and FIG. 29, an information reproducing apparatus 1 g in a seventh modified example will be described. FIG. 28 is a waveform chart conceptually showing an operation of correcting the waveform distortion by a waveform distortion correction circuit 18 g provided for the information reproducing apparatus 1 g in the seventh modified example, on the sample value series RS_(C). FIG. 29 is a block diagram conceptually showing the structure of the waveform distortion correction circuit 18 g provided for the information reproducing apparatus 1 g in the seventh modified example.

Incidentally, the same structures and operations as those in the aforementioned example carry the same reference numerals, and the explanation thereof is omitted.

As shown in FIG. 28, in the seventh modified example, as the distortion correction value amd, a value (i.e. 2 L or −2 L) which is twice the upper limit L or lower limit −L of the amplitude limit value on the limit equalizer 15 (i.e. the lower limit −L of the amplitude limit value for the waveform distortion shown in FIG. 5( a) to FIG. 5( c), and the upper limit L of the amplitude limit value for the waveform distortion shown in FIG. 6( a) to FIG. 6( c)) is used.

In this case, as shown in FIG. 29, the waveform distortion correction circuit 18 g is provided with the delay adjustment circuit 181, an amplifier 182 g, the mark/space length detection circuit 183, the timing generation circuit 184, and the selector 185.

The amplifier 182 g amplifies the upper limit L or lower limit −L of the amplitude limit value on the limit equalizer 15 by two times, and then outputs it to the selector 185 as the distortion correction value amd.

As described above, even if the value which is twice the upper limit L or lower limit −L of the amplitude limit value on the limit equalizer 15 is used as the distortion correction value amd, it is possible to preferably receive the aforementioned various effects.

In addition, since the signal level of the waveform distortion is corrected to the upper limit L or lower limit −L of the amplitude limit value on the limit equalizer 15, it is certainly possible to prevent such a disadvantage that the waveform distortion which is originally not to occur is emphasized. Moreover, it is also possible to preferably prevent such a disadvantage that the mark with a relatively long run length is misjudged to be another mark, caused by the emphasized waveform distortion, in the information reproducing apparatus which adopts the PRML. As a result, the binary error caused by the waveform distortion hardly occurs, which allows the preferable reproduction operation.

Moreover, even if a noise component is superimposed on the read signal R_(RF), since the signal level of the waveform distortion is corrected to the signal level which is less than or equal to the value which is twice the upper limit L or the lower limit −L of the amplitude limit value, it is certainly possible to prevent such a disadvantage that the waveform distortion is less than or equal to the upper limit L of the amplitude limit value or is greater than or equal to the lower limit −L. As a result, it is possible to preferably prevent such a disadvantage that the long mark is misjudged to be another mark. As a result, the binary error caused by the waveform distortion hardly occurs, which allows the preferable reproduction operation.

(9) Eighth Modified Example Increase in Amplification Factor on Pre-Equalizer

Next, with reference to FIG. 30 to FIG. 33, an information reproducing apparatus lh in an eighth modified example will be described. FIG. 30 are graphs showing a change in symbol error rate with respect to asymmetry, in each of a case where the amplification factor of a pre-equalizer 14 h provided for the information reproducing apparatus 1 h in the eighth modified example is increased and a case where the amplification factor is not increased. FIG. 31 are graphs showing a change in symbol error rate with respect to the amplification factor of the pre-equalizer 14 h, in each of a case where the waveform distortion is corrected and a case where the waveform distortion is not corrected. FIG. 32 is a waveform chart conceptually showing a waveform of the read signal R_(RF) corresponding to minT according to a change in asymmetry. FIG. 33 is a waveform chart conceptually showing another waveform or the like of the read signal R_(RF) before and after the correction of the waveform distortion.

In the eighth modified example, the pre-equalizer 14 h can arbitrarily increase (or moreover, reduce) the amplification factor of the pre-equalizer 14 h, in comparison with a reference amplification factor set in advance for the pre-equalizer 14 h. In other words, in the eighth modified example, the waveform distortion is corrected after the amplification factor of the pre-equalizer 14 h is increased, compared to the reference amplification factor set in advance for the pre-equalizer 14 h, and then, the amplitude limit and the high-frequency emphasis are performed on the limit equalizer 15.

Specifically, with respect to the amplification factor of the pre-equalizer 14, if the signal level of a minT space (more specifically, the signal level of the peak of the minT space, i.e. the maximum signal level of the minT space) is less than or equal to the zero level, the amplification factor of the pre-equalizer 14 h is increased, compared to the reference amplification factor set in advance for the pre-equalizer 14 h.

Here, however, the operation example in the case where the zero level is used as the reference level is explained. Thus, in the case where the reference level is not the zero level, the amplification factor of the pre-equalizer 14 h is preferably increased, compared to the reference amplification factor set in advance for the pre-equalizer 14 h, if the signal level of the minT space is less than or equal to the reference level.

Moreover, here, the explanation is given on the operation example in a case where it is aimed at the operation disc 100 in which the reflectance of the laser beam LB is reduced by forming the marks. Therefore, if it is aimed at the operation disc 100 in which the reflectance of the laser beam LB is increased by forming the marks, if the signal level of the minT space (more specifically, the signal level of the peak of the minT space, i.e. the minimum signal level of the minT space) is greater than or equal to the zero level (or the reference level), the amplification factor of the pre-equalizer 14 h is increased, compared to the reference amplification factor set in advance for the pre-equalizer 14 h.

Here, the pre-equalizer 14 h preferably increases the reference amplification factor set in advance for the pre-equalizer 14 h, by approximately 1 dB to 3 dB. Specifically, for example, if the reference amplification factor set in advance for the pre-equalizer 14 h is 5 dB, it is preferable to remove the intersymbol interference (in other words, to perform waveform-shaping) from the read sample value series RS, by using an amplification factor of approximately 6 dB to 8 dB.

Moreover, the pre-equalizer 14 h preferably increases the aforementioned amplification factor when performing the waveform-shaping on a signal component which is at the frequency of the read signal R_(RF) corresponding to the record data with the shortest run length or which is in the vicinity of this frequency. On the other hand, the pre-equalizer 14 h preferably uses the aforementioned reference amplification factor (i.e. does not increase the amplification factor) when performing the waveform-shaping on a signal component other than the signal component which is at the frequency of the read signal R_(RF) corresponding to the record data with the shortest run length or which is in the vicinity of this frequency.

As described above, according to the information reproducing apparatus 1 h in the eighth example, since the amplification factor is increased on the pre-equalizer 14 h before the correction of the waveform distortion, it is possible to receive an effect shown in the following explanation using FIG. 30 to FIG. 33.

Incidentally, in the graphs shown in FIG. 30 and FIG. 31, it is assumed that the reference amplification factor of the pre-equalizer 14 h (i.e. the amplification factor when the amplification factor is not increased) is 5 dB.

As shown in FIG. 30( a), the symbol error rate in the case where the amplification factor is increased to 7.4 dB is improved, compared to the symbol error rate in the case where the amplification factor is not increased (i.e. in the case where the amplification factor is 5.0 dB),

Incidentally, as shown in FIG. 30( b), if the waveform distortion is not corrected, the symbol error rate in the case where the amplification factor is increased to 7.4 dB is deteriorated, compared to the symbol error rate in the case where the amplification factor is not increased (i.e. in the case where the amplification factor is 5.0 dB). This is caused by the amplified waveform distortion due to the increase of the amplification factor. Therefore, it is extremely preferable to perform the waveform distortion in the case where the amplification factor is increased. By this, as shown in FIG. 30( a), the symbol error rate can be improved.

In conclusion, as can be seen from the graph shown in FIG. 30( a), it is possible to improve the symbol error rate by increasing the amplification factor of the pre-equalizer 14 h in a predetermined case. In other words, it is possible to improve reproduction properties. In particular, even if the asymmetry is relatively large, although the symbol error rate is increased in the case where the amplification factor is increased, the value is still improved compared to the symbol error rate in the case where the amplification factor is not increased.

Moreover, as shown in FIG. 31, in the case where the waveform distortion is corrected while fixing the asymmetry to 8%, the symbol error is rate is improved compared to the symbol error rate in the case where the amplification factor of the pre-equalizer 14 h is not increased (i.e. where the amplification factor is 5.0 dB), by increasing the amplification factor of the pre-equalizer 14 h by approximately 1 dB to 3 dB.

Incidentally, as shown in FIG. 31, in the case where the amplification factor of the pre-equalizer 14 h is increased by approximately 3 dB or more, the symbol error rate is deteriorated, compared to the symbol error rate in the case where the amplification factor of the pre-equalizer 14 h is not increased. The deterioration of the symbol error rate is caused by that the waveform distortion is excessively emphasized due to the excessively increased amplification factor and thereby the mark with a relatively long run length in which the waveform distortion occurs is misjudged to be another mark.

As described above, the improvement of the reproduction properties (e.g. the symbol error rate) by increasing the amplification factor of the pre-equalizer 14 h can be explained from the following reasons.

As shown on the upper side of FIG. 32, if it is aimed at the optical disc 100 in which the reflectance of the laser beam LB is reduced by forming the marks, the signal level of the minT space is greater than the signal level of the minT mark. In this case, as the asymmetry increases, the signal waveform of minT is gradually shifted to the lower side (i.e. negative side), with respect to an all T center level (i.e. the reference level or the zero level). If the asymmetry increases to some degree, the signal level of the peak of the minT space likely falls below the all T center level. In this case, the minT is likely misjudged to be the waveform distortion. As a result, as shown in FIG. 33, since the minT is corrected as the waveform distortion, a signal corresponding to the mint does not appear in the binary signal, which leads to the deterioration of the symbol error rate.

In the same manner, as shown on the lower side of FIG. 32, if it is aimed at the optical disc 100 in which the reflectance of the laser beam LB is increased by forming the marks, the signal level of the minT space is less than the signal level of the minT mark. In this case, as the asymmetry increases, the signal waveform of minT is gradually shifted to the upper side (i.e. positive side), with respect to the all T center level (i.e. the reference level or the zero level). If the asymmetry increases to some degree, the signal level of the peak of the minT space likely exceeds the all T center level. In this case, the minT is likely misjudged to be the waveform distortion. As a result, since the minT is corrected as the waveform distortion, the signal corresponding to the minT does not appear in the binary signal, which leads to the deterioration of the symbol error rate.

However, according to the eighth modified example, the signal waveform of the minT can be shifted by increasing the amplification factor of the pre-equalizer 14 h (in particular, by increasing the amplification factor with respect to the signal component which is at the frequency of the read signal R_(RF) corresponding to the record data with the shortest run length and which is in the vanity of the frequency). As a result, it is possible to preferably prevent such a disadvantage that the signal level of the peak of the minT space described above falls below or exceeds the all T center level. As a result, it is possible to preferably prevent the deterioration of the symbol error rate.

Moreover, in the structure shown in FIG. 1, the pre-equalizer 14 is disposed at a subsequent stage of the A/D converter 13; namely, the construction in which the pre-equalizer 14 performs a digital signal process is disclosed. However, obviously, the pre-equalizer 14 may be disposed at a previous stage of the A/D converter 13; namely, the pre-equalizer 14 may perform an analog signal process. Even in this case, obviously, various operations described later can be performed, as in the construction that the pre-equalizer 14 performs the digital signal process.

(10) Ninth Modified Example Addition of Offset

Next, with reference to FIG. 34, an information reproducing apparatus 1 i in a ninth modified example will be described. FIG. 34 is a block diagram conceptually showing the basic structure of the information reproducing apparatus 1 i in the ninth modified example.

As shown in FIG. 34, an information reproducing apparatus 1 i in the ninth modified example is provided with the spindle motor 10, the pickup (PU) 11, the HPF (High Pass Filter) 12, the A/D converter 13, the pre-equalizer 14, the limit equalizer 15, the binary circuit 16, the decoding circuit 17, the waveform distortion correction circuit 18, an adder 19-1 i, an offset generation circuit 19-2 i; and the reproduction property judgment circuit 20.

Incidentally, even in the structure shown in FIG. 34, as in the structure shown in FIG. 1, if the SER is used as the reproduction property of the read signal R_(RF), the aforementioned decoding circuit 17 preferably performs an error correction process in addition to the decoding process; namely, if the SER is used as the reproduction property of the read signal R_(RF), the aforementioned decoding circuit 17 is preferably a decoding/correction circuit 17.

The adder 19-1 i adds an offset value OFS generated on the offset generation circuit, to the read sample value series RS_(C) outputted from the pre-equalizer 14. The read sample value series RS_(C) with the offset value OFS added is outputted to the waveform distortion correction circuit 18.

The offset generation circuit 19-2 i generates the offset value OFS. Incidentally, the offset value OFS will be detailed later (refer to FIG. 35 and subsequent drawings).

More specifically, in the reproduction operation, by the operation of the offset generation circuit 19-2 i, the offset value OFS is added to the read signal R_(RF) (and more specifically, the read sample value series RS_(C)). In this case, for example, the offset value OFS may be added if an α value described later is not substantially 0, and the offset value OFS may be not added if the α value described later is substantially 0. Alternatively, for example, the offset value OFS may be added if the symbol error rate is greater than or equal to a predetermined threshold value, or if the error correction is unable to be performed, or if the synchronization data is unable to be read, and the offset value OFS may be not added if the symbol error rate is not greater than or equal to a predetermined threshold value, and if the error correction is not unable to be performed, and if the synchronization data is not unable to be read.

As described above, in the ninth modified example, since the offset value OFS is added to the read signal R_(RF) (and more specifically, the read sample value series RS_(C)) before the waveform distortion is corrected, the following effect can be also received. Hereinafter, with reference to FIG. 35 to FIG. 43, an explanation will be given on the effect obtained by adding the offset value OFS, as well as the explanation of generating operation of the offset value OFS.

(10-1) Addition of Offset Value OFS Based on Asymmetry Value

Firstly, an explanation will be given on the addition of the offset value OFS based on an asymmetry value, with reference to FIG. 35 to FIG. 38. FIG. 35 is a waveform chart conceptually showing an asymmetry value. FIG. 36 are graphs showing a change in symbol error rate with respect to the offset value OFS normalized by the amplitude of the read signal R_(RF). FIG. 37 are graphs showing a change in the offset value normalized by the amplitude of the read signal R_(RF), with respect to the asymmetry value. FIG. 38 are tables showing the appearance probability of the record data with each run length.

As shown in FIG. 35, the asymmetry value indicates the deviation of the amplitude center of the read signal corresponding to the record data with the shortest run length, with respect to the amplitude center of the read signal R_(RF) corresponding to the record data with the longest run length. Specifically, the asymmetry value Asy=((ImaxH+ImaxL)−(IminH+IminL))/(2×(ImaxH+ImaxL)), wherein the amplitude center of the read signal R_(RF) corresponding to the data with the longest run length is ImaxCnt, ImaxH is the magnitude of the top amplitude of the read signal R_(RF) corresponding to the data with the longest run length based on ImaxCnt, ImaxL is the magnitude of the bottom amplitude of the read signal R_(RF) corresponding to the data with the longest run length based on ImaxCnt, IminH is the magnitude of the top amplitude of the read signal R_(RF) corresponding to the data with the shortest run length based on ImaxCnt, and IminL is the magnitude of the bottom amplitude of the read signal R_(RF) corresponding to the data with the shortest run length based on ImaxCnt. Incidentally, ImaxCnt is an average value of the top amplitude value and the bottom amplitude value of the read signal R_(RF) corresponding to the data with the longest run length.

As shown in FIG. 36( a), if the asymmetry value is 6% in a Blu-ray Disc, which is one specific example of the optical disc 100, the symbol error rate in the case where the offset value OFS is added is improved when the offset value OFS normalized by the amplitude of the read signal R_(RF) is about 0% to 5%, compared to the symbol error rate in the case where the offset value OFS is not added. In particular, when the offset value OFS normalized by the amplitude of the read signal R_(RF) is about 2%, the symbol error rate is minimal.

Incidentally, note that an entire β value described later is 9.3%, a partial β value is 10.0%, and an α value is −3.0%, when the symbol error rate is minimal.

As shown in FIG. 36( b), if the asymmetry value is 8% in a Blu-ray Disc, which is one specific example of the optical disc 100, the symbol error rate in the case where the offset value OFS is added is improved when the offset value OFS normalized by the amplitude of the read signal R_(RF) is about 0% to 7%, compared to the symbol error rate in the case where the offset value OFS is not added. In particular, when the offset value OFS normalized by the amplitude of the read signal R_(RF) is about 3%, the symbol error rate is minimal.

Incidentally, note that the entire β value described later is 12.3%, the partial β value is 14.0%, and the α value is −4.4%, when the symbol error rate is minimal.

As shown in FIG. 36( c), if the asymmetry value is 11% in a Blu-ray Disc, which is one specific example of the optical disc 100, the symbol error rate in the case where the offset value OFS is added is improved when the offset value OFS normalized by the amplitude of the read signal R_(RF) is about 0% to 9%, compared to the symbol error rate in the case where the offset value OFS is not added. In particular, when the offset value OFS normalized by the amplitude of the read signal R_(RF) is about 4%, the symbol error rate is

Incidentally, note that the entire β value described later is 15.0%, the partial β value is 19.0%, and the α value is −5.4%, when the symbol error rate is minimal.

As described above, it can be seen that the symbol error rate in the case where the offset value OFS is added is improved, compared to the symbol error rate in the case where the offset value OFS is not added. In particular, it can be seen that the symbol error rate is improved by adding the offset value OFS with the same polarity as that of the asymmetry.

FIG. 37 shows a graph obtained by plotting the asymmetry values and the offset values OFS when the symbol error rate is minimal, shown in FIG. 36(a) to FIG. 36( c). As shown in FIG. 37, the offset value OFS normalized by the amplitude of the read signal R_(RF) is expressed by OFS=0.3947×asymmetry −0.2895.

Now, the appearance probability, which does not consider the run length, of the record data with each run length, which is shown in FIG. 38( a) and FIG. 38( b), will be focused on.

FIG. 38( a) shows the appearance probability, which considers the run length, of the record data with each run length in 1 ECC block if random data is recorded onto a Blu-ray Disc, which is one specific example of the optical disc 100. As shown in FIG. 38( a), in 1 ECC block, the appearance probability of the record data with a run length of 2 T is about 38%, the appearance probability of the record data with a run length of 3 T is about 25%, the appearance probability of the record data with a run length of 4 T is about 16%, the appearance probability of the record data with a run length of 5 T is about 10%, the appearance probability of the record data with a run length of 6 T is about 6%, the appearance probability of the record data with a run length of 7 T is about 3%, the appearance probability of the record data with a run length of 8 T is about 1.6%, and the appearance probability of the record data with a run length of 9 T is about 0.35%.

Incidentally, the appearance probability shown here (the T appearance probability in FIG. 38) is the appearance probability which does not consider the run length. In other words, weighting is the same, which is used to calculate the appearance probability in each of the record data with a run length of 2 T, the record data with a run length of 3 T, the record data with a run length of 4 T, the record data with a run length of 5 T, the record data with a run length of 6 T, the record data with a run length of 7 T, the record data with a run length of 8 T, and the record data with a run length of 9 T. In other words, it indicates the appearance probability when the number of appearances is counted as one if one record data with a certain run length appears.

In considering the appearance probability and the graph (or equation) shown in FIG. 37, the coefficient, 0.3947, which is multiplied with the asymmetry in the equation for obtaining the offset value shown in FIG. 37 can be considered to be substantially same as the appearance probability, 38% (0.3809) of the record data with a run length of 2 T. Thus, the offset value OFS normalized by the amplitude of the read signal R_(RF) can be approximated by a value which is obtained by multiplying the appearance probability, which does not consider the run length, of the record data with the shortest run length with the asymmetry value. In other words, in a Blu-ray Disc, which is one specific example of the optical disc 100, the offset value OFS normalized by the amplitude of the read signal R_(RF) can be approximated by 0.3809×the asymmetry value.

Moreover, FIG. 38( b) shows the appearance probability, which does not consider the run length, of the record data with each run length in 1ECC block if the random data is recorded onto a DVD, which is one specific example of the optical disc 100. As shown in FIG. 38( b), in 1ECC block, the appearance probability of the record data with a run length of 3 T is about 32%, the appearance probability of the record data with a run length of 4 T is about, 24%, the appearance probability of the record data with a run length of 5 T is about 17%, the appearance probability of the record data with a run length of 6 T is about 11.5%, the appearance probability of the record data with a run length of 7 T is about 7%, the appearance probability of the record data with a run length of 8 T is about 4%, the appearance probability of the record data with a run length of 9 T is about 2%, the appearance probability of the record data with a run length of 10 T is about 1.3%, the appearance probability of the record data with a run length of 11 T is about 0.24%, and the appearance probability of the record data with a run length of 14 T is about 0.3%. Even in this case, the offset value OFS normalized by the amplitude of the read signal R_(RF) can be approximated by the value which is obtained by multiplying the appearance probability, which does not consider the run length, of the record data with the shortest run length, by the asymmetry value. In other words, in a DVD, which is one specific example of the optical disc 100, the offset value OFS normalized by the amplitude of the read signal R_(RF) can be approximated by 0.3184×the asymmetry value.

Of course, in optical discs other than a Blu-ray Disc and a DVD, in the same manner, the offset value OFS normalized by the amplitude of the read signal R_(RF) can be approximated by the appearance probability not considering the run length, of the record data with the shortest run length×the asymmetry value.

As explained above, the offset generation circuit 19-2 i generates the offset value OFS on the basis of the asymmetry value. As described above, the improvement of the reproduction properties (e.g. the symbol error rate) by adding the offset value OFS can be explained from the same reasons as those already described using FIG. 32 and FIG. 33. Specifically, according to the ninth modified example, by adding the offset value OFS, it is possible to shift the signal waveform of the minT. As a result, it is possible to preferably prevent such a disadvantage that the signal level of the peak of the minT space falls below or exceeds the all T center level. As a result, it is possible to preferably prevent the deterioration of the symbol error rate.

(10-2) Addition of Offset Value OFS Based on Entire β Value

Next, an explanation will be given on the addition of the offset value OFS based on an entire β value, with reference to FIG. 39 and FIG. 40. FIG. 39 is a waveform chart conceptually showing the entire β value. FIG. 40 is a graph showing a change in the offset value normalized by the amplitude of the read signal R_(RF), with respect to the entire β value normalized by the amplitude of the read signal R_(RF).

As shown in FIG. 39, the entire β value indicates the average position of the amplitude center of the read signals R_(RF) corresponding to the respective record data with all types of run lengths (e.g. the record data with each of run lengths of 3 T to 11 T and 14 T if the optical disc 100 is a DVD, and the record data with each of run lengths of 2 T to 9 T if the optical disc 100 is a Blu-ray Disc). Specifically, entire β value=(A1+A2)/(A1−A2), wherein A1 is the magnitude of the maximum amplitude (top amplitude) on the upper side (positive side) which is based on the amplitude center (i.e. all T center level) of the read signals R_(RF) corresponding to the record data with all types of run lengths (i.e. the amplitude center is set at the origin or base point) and A2 is the magnitude of the maximum amplitude (bottom amplitude) on the lower side (negative side) which is based on the amplitude center of the read signals R_(RF) corresponding to the record data with all types of run lengths.

FIG. 40 shows a graph obtained by plotting the entire β values and the offset values OFS when the symbol error rate is minimal, shown in FIG. 36( a) to FIG. 36( c). As shown in FIG. 40, the offset value OFS normalized by the amplitude of the read signal R_(RF) is expressed by OFS=0.3506×entire β value −1.2768.

In considering the appearance probability shown in FIG. 38 and the graph (or equation) shown in FIG. 40, the coefficient, 0.3506, multiplied with the entire β value in the equation for obtaining the offset value shown in FIG. 40 and the appearance probability, 38% (0.3809), of the record data with a run length of 2 T can be considered to be substantially the same value. Thus, the offset value OFS normalized by the amplitude of the read signal R_(RF) can be approximated by a value which is obtained by multiplying the appearance probability of the record data with the shortest run length by the entire β value. In other words, in a Blu-ray Disc, which is one specific example of the optical disc 100, the offset value OFS normalized by the amplitude of the read signal R_(RF) can be approximated by 0.3809×the entire β value.

In the same manner, in a DVD, which is one specific example of the optical disc 100, the offset value OFS normalized by the amplitude of the read signal R_(RF) can be approximated by 0.3184×the entire β value.

Of course, in optical discs other than a Blu-ray Disc and a DVD, in the same manner, the offset value OFS normalized by the amplitude of the read signal R_(RF) can be approximated by the appearance probability, which does not consider the run length, of the record data with the shortest run length×the entire β value.

As explained above, the offset generation circuit 19-2 i generates the offset value OFS on the basis of the entire β value. Even if the offset value OFS is generated on the basis of the entire β value, it is possible to preferably receive the same effect as that in the case where the offset value OFS is generated on the basis of the asymmetry value.

(10-3) Addition of Offset Value OFS Based on Partial β Value

Next, an explanation will be given on the addition of the offset value OFS based on a partial β value, with reference to FIG. 41 and FIG. 42. FIG. 41 is a waveform chart conceptually showing the partial β value. FIG. 42 is a graph showing a change in the offset value normalized by the amplitude of the read signal R_(RF), with respect to the partial β value normalized by the amplitude of the read signal R_(RF).

As shown in FIG. 41, the partial β value indicates the deviation between the amplitude center of the read signal R_(RF) corresponding to the record data with the shortest run length and the amplitude center of the read signal R_(RF) corresponding to the record data with the second shortest run length. Specifically, the partial β value=(Imin+1 H+Imin+1 L)/(Imin+1 H−Imin+1 L), wherein the amplitude center of the read signal corresponding to the record data with the shortest run length is IminCnt, Imin+1 H indicates the magnitude of the top amplitude of the read signal R_(RF) corresponding to the record data with the second shortest run length based on IminCnt, and Imin+1 L indicates the magnitude of the bottom amplitude of the read signal R_(RF) corresponding to the record data with the second shortest run length based on IminCnt. Incidentally, IminCnt is an average value of the top amplitude value IminH and the bottom amplitude value IminL of the read signal R_(RF) corresponding to the record data with the shortest run length.

FIG. 42 shows a graph obtained by plotting the partial β values and the offset values OFS when the symbol error rate is minimal, shown in FIG. 36( a) to FIG. 36( c). As shown in FIG. 42, the offset value OFS normalized by the amplitude of the read signal R_(RF) is expressed by OFS=0.2213×partial β value−0.1721.

Now, the appearance probability, which considers the run length, of the record data with each run length, which is shown in FIG. 38( a) and FIG. 38( b), will be focused on.

FIG. 38( a) shows the appearance probability, which considers the run length, of the record data with each run length in 1ECC block if random data is recorded onto a Blu-ray Disc, which is one specific example of the optical disc 100. As shown in FIG. 38( a), in 1ECC block, the appearance probability of the record data with a run length of 2 T is about 22%, the appearance probability of the record data with a run length of 3 T is about 22%, the appearance probability of the record data with a run length of 4 T is about 19%, the appearance probability of the record data with a run length of 5 T is about 14%, the appearance probability of the record data with a run length of 6 T is about 10%, the appearance probability of the record data with a run length of 7 T is about 6%, the appearance probability of the record data with a run length of 8 T is about 4%, and the appearance probability of the record data with a run length of 9 T is about 0.9%.

Incidentally, the appearance probability shown here (the sample appearance probability in FIG. 38) is the appearance probability, which considers the run length. In other words, weighting is in proportion to the run length, which is used to calculate the appearance probability in each of the record data with a run length of 2 T, the record data with a run length of 3 T, the record data with a run length of 4 T, the record data with a run length of 5 T, the record data with a run length of 6 T, the record data with a run length of 7 T, the record data with a run length of 8 T, and the record data with a run length of 9 T. In other words, it indicates the appearance probability in the case where the number of appearances is counted as n if one record data with a run length of nT appears (i.e. if one record data including n sample values by sampling appears).

In considering the appearance probability and the graph (or equation) shown in FIG. 42, the coefficient, 0.2213, which is multiplied with the partial β value in the equation for obtaining the offset value shown in FIG. 42 can be considered to be substantially same as the appearance probability, 22% (0.2255), of the record data with a run length of 2 T. Thus, the offset value OFS normalized by the amplitude of the read signal R_(RF) can be approximated by a value which is obtained by multiplying the appearance probability, which considers the run length, of the record data with the shortest run length, by the partial β value. In other words, in a Blu-ray Disc, which is one specific example of the optical disc 100, the offset value OFS normalized by the amplitude of the read signal R_(RF) can be approximated by 0.2255×the partial β value.

Moreover, FIG. 38( b) shows the appearance probability, which considers the run length, of the record data with each run length in 1ECC block if the random data is recorded onto a DVD, which is one specific example of the optical disc 100. As shown in FIG. 38( b), in 1ECC block, the appearance probability of the record data with a run length of 3 T is about 20%, the appearance probability of the record data with a run length of 4 T is about 20%, the appearance probability of the record data with a run length of 5 T is about 18%, the appearance probability of the record data with a run length of 6 T is about 14%, the appearance probability of the record data with a run length of 7 T is about 10%, the appearance probability of the record data with a run length of 8 T is about 7%, the appearance probability of the record data with a run length of 9 T is about 4.5%, the appearance probability of the record data with a run length of 10 T is about 3%, the appearance probability of the record data with a run length of 11 T is about 0.5%, and the appearance probability of the record data with a run length of 14 T is about 0.9%. Even in this case, the offset value OFS normalized by the amplitude of the read signal R_(RF) can be approximated by the value which is obtained by multiplying the appearance probability, which considers the run length, of the record data with the shortest run length by the partial β value. In other words, in a DVD, which is one specific example of the optical disc 100, the offset value OFS normalized by the amplitude of the read signal R_(RF) can be approximated by 0.2026×the partial β value.

Of course, in optical discs other than a Blu-ray Disc and a DVD, in the same manner, the offset value OFS normalized by the amplitude of the read signal R_(RF) can be approximated by the appearance probability, which considers the run length, of the record data with the shortest run length×the partial β value.

As explained above, the offset generation circuit 19-2 i generates the offset value on the basis of the partial β value. Even if the offset value OFS is generated on the basis of the partial β value, it is possible to preferably receive the same effect as that in the case where the offset value OFS is generated on the basis of the asymmetry value.

(10-4) Addition of Offset Value OFS Based on α Value

Next, an explanation will be given on the addition of the offset value OFS based on an a value, with reference to FIG. 43. FIG. 43 is a waveform chart conceptually showing the α value.

As shown in FIG. 43, the α value indicates a deviation ratio (or rate) of the amplitude center of the read signal R_(RF) corresponding to the record data with the shortest run length, with respect to the amplitude center (i.e. the reference level, and the zero level in the example) of the read signals R_(RF) corresponding to the respective record data with all types of run lengths (e.g. the record data with each of run lengths of 3 T to 11 T and 14 T if the optical disc 100 is a DVD, and the record data with each of run lengths of 2 T to 9 T if the optical disc 100 is a Blu-ray Disc). Specifically, a value=Δ Ref/(ImaxH−ImaxL), wherein ImaxH is the magnitude of the top amplitude of the read signal R_(RF) corresponding to the data with the longest run length based on the amplitude center of the read signal R_(RF) corresponding to the record data with all types of run lengths (i.e. all T center level), ImaxL is the magnitude of the bottom amplitude of the read signal R_(RF) corresponding to the data with the longest run length based on the amplitude center of the read signals R_(RF) corresponding to the record data with all types of run lengths (i.e. all T center level), and Δ Ref is a shift amount of the amplitude center of the read signal R_(RF) corresponding to the record data with the shortest run length, with respect to the amplitude center of the read signals R_(RF) corresponding to the record data with all types of run lengths.

In this case, the offset generation circuit 19-2 i outputs the α value to the adder 19-1 i as the offset value OFS; namely, the offset generation circuit 19-2 i generates the α value itself. As described above, even if the offset value OFS is generated on the basis of the α value, it is possible to preferably receive the same effect as that in the case where the offset value OFS is generated on the basis of the asymmetry value.

(11) Tenth Modified Example Addition and Subtraction of Offset

Next, with reference to FIG. 44 and FIG. 45, an information reproducing apparatus 1 j in a tenth modified example will be described. FIG. 44 is a block diagram conceptually showing the basic structure of the information reproducing apparatus in the tenth modified example. FIG. 45 are graphs showing a change in symbol error rate with respect to the offset value normalized by the amplitude of the read signal, in each of a case where the offset value OFS is only added (i.e. where the offset value OFS is not subtracted) and a case where the offset value OFS is added and subtracted.

As shown in FIG. 44, the information reproducing apparatus 1 j in the tenth modified example is provided with a spindle motor 10, a pickup (PU) 11, a HPF (High Pass Filter) 12, an A/D converter 13, a pre-equalizer 14, a limit equalizer 15, a binary circuit 16, a decoding circuit 17, a waveform distortion correction circuit 18, an adder 19-1 j, an offset generation circuit 19-2 j; a subtracter 19-3 j; and a reproduction property judgment circuit 20.

Incidentally, even in the structure shown in FIG. 44, as in the structure shown in FIG. 1, if the SER is used as the reproduction property of the read signal R_(RF), the aforementioned decoding circuit 17 preferably performs an error correction process in addition to the decoding process; namely, if the SER is used as the reproduction property of the read signal R_(RF), the aforementioned decoding circuit 17 is preferably a decoding/correction circuit 17.

The adder 19-1 j adds an offset value OFS generated on the offset generation circuit, to the read sample value series RS_(C) outputted from the pre-equalizer 14. The read sample value series RS_(C) with the offset value OFS added is outputted to the waveform distortion correction circuit 18.

The offset generation circuit 19-2 j generates the offset value OFS. The subtracter 19-3 j subtracts the offset value OFS generated on the offset generation circuit 19-2 j, from the distortion-corrected read sample value series RS_(CAM). The distortion-corrected read sample value series RS_(CAM) with the offset value OFS subtracted is outputted to the limit equalizer 15.

More specifically, in the reproduction operation, by the operation of the offset generation circuit 19-2 j, the offset value OFS is added to the read signal R_(RF) (and more specifically, the read sample value series RS_(C)). In this case, for example, the offset value OFS may be added if the α value is not substantially 0, and the offset value OFS may be not added if the α value is substantially 0. Alternatively, for example, the offset value OFS may be added if the symbol error rate is greater than or equal to a predetermined threshold value, or if the error correction is unable to be performed, or if the synchronization data is unable to be read, and the offset value OFS may be not added if the symbol error rate is not greater than or equal to a predetermined threshold value, and if the error correction is not unable to be performed, and if the synchronization data is not unable to be read.

As described above, in the ninth modified example, since the offset value OFS is added to the read signal R_(RF) (and more specifically, the read sample value series RS_(C)) before the correction of the waveform distortion, it is possible to further receive the following effect. Hereinafter, with reference to

FIG. 35 to FIG. 43, the effect obtained by adding the offset value OFS will be described, together with an operation of generating the offset value OFS.

The offset value OFS generated in the tenth modified example is preferably less than a difference (i.e. the waveform distortion amount D′) between the reference level and the maximum value of the signal level of the long mark in which the waveform distortion occurs, if the waveform distortion occurs as shown in FIG. 5( a) to FIG. 5( c). More preferably, it is preferably less than a half of the difference (i.e. the waveform distortion amount D′) between the reference level and the maximum value of the signal level of the long mark in which the waveform distortion occurs. In other words, offset is generated in a direction of the waveform distortion approaching the reference level.

The offset value OFS generated in the tenth modified example is preferably less than a difference (i.e. the waveform distortion amount—D′) between the reference level and the minimum value of the signal level of the long mark in which the waveform distortion occurs, if the waveform distortion occurs as shown in FIG. 6( a) to FIG. 6( c). More preferably, it is preferably less than a half of the difference (i.e. the waveform distortion amount—D′) between the reference level and the minimum value of the signal level of the long mark in which the waveform distortion occurs. In other words, the offset is generated in the direction of the waveform distortion approaching the reference level.

Then, after the correction of the waveform distortion, the offset value OFS is subtracted from the distortion-corrected read sample value series RS_(CAM); namely, the offset value OFS which is the same as that added before the correction of the waveform distortion is subtracted from the distortion-corrected read sample value series RS_(CAM).

As described above, in the tenth modified example, since the offset value OFS is added to the read signal R_(RF) (and more specifically the read sample value series RS_(C)) before the waveform distortion is corrected, and the added offset value OFS is subtracted after the waveform distortion is corrected, it is possible to further receive an effect which is hereinafter explained with reference to FIG. 45.

As shown in FIG. 45, it can be seen that a range of the offset value OFS, which improves the symbol error rate in the case where the offset value OFS is added and subtracted, is expanded, compared to a range of the offset value OFS which improves the symbol error rate in the case where the offset value OFS is only added. In other words, by adding and subtracting the offset value OFS, it is possible to expand the range of the offset value OFS which can preferably improves the symbol error rate.

Moreover, since the same offset value OFS is subtracted after the correction of the waveform distortion, it is also possible to receive such an effect that the offset value OFS can be relatively easily generated.

Incidentally, in the aforementioned example, the offset value OFS added before the correction of the waveform distortion is same as the offset value OFS subtracted after the correction of the waveform distortion; however, the offset value OFS added before the correction of the waveform distortion is not necessarily same as the offset value OFS subtracted after the correction of the waveform distortion are not necessarily the same. In this case, the offset value OFS added before the correction of the waveform distortion is preferably greater than the offset value OFS subtracted after the correction of the waveform distortion, approximately by a value which is obtained by multiplying the appearance probability of mint, which does not consider the run length, by the entire β value explained with reference to FIG. 39 (or a value which is obtained by multiplying the appearance probability of mint which does not consider the run length by the asymmetry explained with reference to FIG. 35, or a value which is obtained by multiplying the appearance probability of mint which considers the run length by the partial β value explained with reference to FIG. 41, or a value corresponding to the α value explained with reference to FIG. 43).

As described above, by increasing the offset value OFS added before the correction of the waveform distortion by the magnitude corresponding to the value determined in accordance with the asymmetry value, the entire β value, or the partial β value, compared to the offset value OFS subtracted after the correction of the waveform distortion, it is possible to leave an offset component with the aforementioned magnitude corresponding to the value determined in accordance with the asymmetry value, the entire β value, or the partial β value, in the distortion-corrected read sample value series RS_(CAM) after the correction of the waveform distortion. This allows the amplitude center of the read signal R_(RF) corresponding to the record data with the shortest run length to match the reference level, in the distortion-corrected read sample value series RS_(CAM) after the correction of the waveform distortion.

Incidentally, the waveform distortion occurs generally due to the dispersion of the shape, length, and the like of the marks formed on the recording surface of the optical disc 100. Therefore, the waveform distortion tends to occur in the recording type optical disc 100, such as a DVD-R/RW, a DVD+R/RW, a DVD-RAM, and a BD-R/RE. However, even in the read-only type optical disc 100, such as a DVD-ROM and a BD-ROM, the waveform distortion occurs if the synchronization data formed of the relatively long mark is adjacent to each other in a tracking direction, as shown in FIG. 46. For the waveform distortion occurring in the read-only type optical disc 100, according to the information reproducing apparatus 1 described above, the correction can be preferably made, obviously.

The present invention is not limited to the aforementioned example, but various changes may be made, if desired, without departing from the essence or spirit of the invention which can be read from the claims and the entire specification. An information reproducing apparatus and method, and a computer program, all of which involve such changes, are also intended to be within the technical scope of the present invention. 

1. An information reproducing apparatus comprising: a judging device for judging whether or not a read signal read from a recording medium satisfies a desired reproduction property; a correcting device for correcting waveform distortion occurring in a read signal corresponding to at least a long mark, of the read signal if it is judged by said judging device that the read signal does not satisfy the desired reproduction property; and a waveform equalizing device for performing a waveform equalization process on the read signal in which the waveform distortion is corrected.
 2. The information reproducing apparatus according to claim 1, further comprising a detecting device for detecting the waveform distortion, said correcting device correcting the waveform distortion if it is judged by said judging device that the read signal does not satisfy the desired reproduction property and if the waveform distortion is detected by said detecting device.
 3. The information reproducing apparatus according to claim 1, wherein said judging device judges that the read signal satisfies the desired reproduction property in at least one of (i) a case where an error correction of the read signal cannot be performed, (ii) a case where an error rate of the read signal is greater than or equal to a predetermined threshold value, or (iii) a case where a read signal corresponding to synchronization data cannot be read, the synchronization data being used to read user data included in record data, the synchronization data being included in the record data.
 4. The information reproducing apparatus according to claim 1, wherein said judging device judges whether or not the read signal satisfies the desired reproduction property after the waveform distortion is corrected by said correcting device, and said correcting device corrects the waveform distortion again if it is judged again by said judging device that the read signal does not satisfy the desired reproduction property.
 5. The information reproducing apparatus according to claim 4, wherein said correcting device corrects the waveform distortion again by using a second waveform distortion correction condition which is different from a first waveform distortion correction condition used when the waveform distortion is corrected at a previous time, if it is judged again by said judging device that the read signal does not satisfy the desired reproduction property.
 6. The information reproducing apparatus according to claim 1, wherein said correcting device corrects the waveform distortion occurring in the read signal corresponding to synchronization data, the synchronization data being used to read user data included in record data, the synchronization data being included in the record data.
 7. The information reproducing apparatus according to claim 6, wherein said correcting device corrects the waveform distortion at least one of before a space which makes a pair with a mark which constitutes the synchronization data of the read signal, after the space, and at a position which satisfies periodicity of the synchronization data with a base point at the space.
 8. The information reproducing apparatus according to claim 7, wherein if the recording medium is a Blu-ray Disc, said correcting device corrects the waveform distortion at least one of before a space with a run length of 9 T which makes a pair with a mark with a run length of 9 T which constitutes the synchronization data of the read signal, after the 9 T space, and at a position after a lapse of a time corresponding to a run length of about 1932 T from the 9 T space.
 9. The information reproducing apparatus according to claim 7, wherein if the recording medium is a DVD, said correcting device corrects the waveform distortion at a position after a lapse of a time corresponding to a run length of about 1488 T from a space with a run length of 14 T which constitutes the synchronization data of the read signal.
 10. The information reproducing apparatus according to claim 1, wherein said waveform equalizing device comprises: an amplitude limiting device for limiting an amplitude level of the read signal in which the waveform distortion is corrected, by a predetermined amplitude limit value, thereby obtaining an amplitude limit signal; and a filtering device for performing a high-frequency emphasis filtering process on the amplitude limit signal, thereby obtaining an equalization-corrected signal.
 11. The information reproducing apparatus according to claim 1, wherein the long mark is a mark whose signal level is maximum amplitude.
 12. An information reproducing method comprising: a judging process of judging whether or not a read signal read from a recording medium satisfies a desired reproduction property; a correcting process of correcting waveform distortion occurring in a read signal corresponding to at least a long mark, of the read signal if it is judged in said judging process that the read signal does not satisfy the desired reproduction property; and a waveform equalizing process of performing a waveform equalization process on the read signal in which the waveform distortion is corrected.
 13. A computer readable recording medium recording thereon a computer program for reproduction control and for controlling a computer provided in an information reproducing apparatus comprising: a judging device for judging whether or not a read signal read from a recording medium satisfies a desired reproduction property; a correcting device for correcting waveform distortion occurring in a read signal corresponding to at least a long mark, of the read signal if it is judged by said judging device that the read signal does not satisfy the desired reproduction property; and a waveform equalizing device for performing a waveform equalization process on the read signal in which the waveform distortion is corrected, said computer program making the computer function as at least one portion of said judging device, said correcting device, and said waveform equalizing device. 